A Landmark Edition on Croatia's Stunning Peninsula
The Istria 100 by UTMB returns this weekend for its 13th edition and 5th as part of the UTMB World Series. From April 10 to 12, nearly 3,200 runners will take on five distances across the heart-shaped Istrian peninsula in northwest Croatia, weaving through medieval hilltop villages, dense forests, rugged canyons, and coastal panoramas.
This event is part of a UTMB World Series triple-header weekend, running alongside Ultra-Trail Mogan by UTMB (making its debut in Zhejiang, China) and the Desert Rats Trail Running Festival by UTMB in Colorado, which we also cover in a dedicated preview.
The Races at a Glance
Istria 100 by UTMB offers five courses, each starting from a different iconic Istrian town and finishing in the coastal city of Umag:
- 168K (100 Miles) - 168.2 km / 7,140 m D+ - Starts Friday April 10 at 17:00 from Labin - 45h cutoff
- 110K - 111.4 km / 4,074 m D+ - Starts Saturday April 11 at 07:00 from Buzet - 28h cutoff
- 69K - 69.6 km / 2,331 m D+ - Starts Saturday April 11 at 09:00 from Buzet - 15h cutoff
- 42K - 42 km / 1,100 m D+ - Starts Saturday April 11 at 12:00 from Motovun
- 21K - 21 km / 150 m D+ - Starts Sunday April 12 at 10:00 from Groznjan
The Hardest Section: Climbing Ucka Mountain
The 168K is described by organizers as "the hardest and the most beautiful course" on offer, and the crux comes early. After departing from the 3,000-year-old town of Labin at dusk, runners face a relentless night climb up Mount Ucka, the highest peak on the Istrian peninsula. The ascent delivers breathtaking views over the Kvarner Bay and the Adriatic Sea, but it also demands careful pacing. With technical, rocky terrain underfoot and over 7,100 meters of total elevation gain ahead, runners who push too hard on Ucka often pay the price later. In 2025, the 168K saw a 29% DNF rate.
After descending to Buzet, where relay bags are available, the route continues through Istria's interior, passing the medieval gem of Motovun before heading west toward the finish in Umag. The terrain throughout combines rocky singletrack, muddy forest paths, old train routes, stream crossings, and stretches of coasteering that make this race uniquely varied.
On the 110K, the first 20 kilometers of Istrian inland trails from Buzet merge with the 168K course for the climb to Istria's highest ridgelines, making this the decisive section for the shorter distance as well.
Our Favorites and Elite Runners to Watch
168K - Men
The top-ranked elite on the 168K startlist is Mark Darbyshire (United Kingdom, UTMB Index 880), who arrives as the clear favorite on paper. Behind him, Bartosz Gorczyca (Poland, Index 855) of team Grupa Luktrans will be a serious threat, while Finnish runner Juuso Simpanen (Index 819, team VJ/Rab/Suunto) and German Johannes Low (Index 817, Salomon Running Team) complete a strong top four. Also watch for Admire Muzopambwa (Zimbabwe, Index 806, Asics Fuji Trail Team), bringing international flair and a high index to this European-heavy field, and David Phillips (United Kingdom, Index 802).
With 2025 champion Alexander Westenberger (Germany) not on the startlist, the race is wide open for a new winner.
168K - Women
Martina Klancnik Potrc (Slovenia, UTMB Index 713, Kailas Fuga) holds the highest index in the women's field and will benefit from racing close to home. Close behind on the startlist, Hana Vachova (Czech Republic, Index 702) and Joanna Tallmann (Germany, Index 702, Team Falke) are separated by the thinnest of margins and should produce a thrilling battle for the podium. Finnish athlete Eevi Bengs (Index 689, Team Altra) and Lenka Hiklova (Slovakia, Index 644), who took third in 2025, round out the favorites.
Defending champion Ivana Siric (Croatia) is absent from the startlist, leaving the women's race without a clear pre-race favorite.
110K - Men
The 110K men's field is exceptionally competitive, led by a trio of high-index runners. Zan Zepic (Slovenia, Index 850), who won this race last year in a blistering 09:56:14, returns to defend his title. Italian duo Riccardo Montani (Index 849, Team Vibram) and Gionata Cogliati (Index 847, Kailas) will push him hard, while Slovak Patrik Milata (Index 840, Hoka) and Italian Stefan Ungericht (Index 837, Dynafit) complete a deep field.
110K - Women
Anna-Stiina Erkkila (Finland, Index 760, Asics Trail Team) leads the women's 110K field. Italian twins Enrica Dematteis (Index 715) and Luisa Dematteis (Index 695) will race together, while Canadian Genevieve Asselin-Demers (Index 704, Naak Pro/Craft Trail/Garmin), who balances racing with motherhood and recovery from an epilepsy diagnosis, brings both talent and an inspiring story.
69K Highlights
The 69K boasts the weekend's highest single UTMB Index with Andrzej Witek (Poland, Index 912, Asics Fuji Trail) heading the men's race, closely followed by Gianluca Ghiano (Italy, Index 906, Brooks Trail Runners). In the women's race, Rosanna Buchauer (Germany, Index 764, Dynafit) is the one to beat, with 2025 110K champion Nicol Guidolin (Italy, Index 696, Fuga Mountain Club) dropping down in distance this year.
42K Highlights
The 42K features Swiss powerhouse Roberto Delorenzi (Index 920, Brooks Trail Runners) with the second-highest index of the entire event, and Italian Lorenzo Beltrami (Index 895, Team Scarpa/Compressport). In the women's race, Camilla Magliano (Italy, Index 765, Kailas Fuga) leads ahead of American Emily Schmitz (Index 724).
Weather Forecast: Near-Perfect Conditions
Runners are in luck this weekend. The forecast for the Istrian peninsula looks almost ideal for ultra-distance racing:
- Friday April 10 (168K start): Overcast, highs of 17C / lows of 8C, winds at 9 km/h, only 3% chance of precipitation
- Saturday April 11 (110K, 69K, 42K start): Overcast, 18C / 10C, winds at 10 km/h, 0% chance of rain
- Sunday April 12 (21K start, 168K finishers): Mostly cloudy, 19C / 9C, gentle 7 km/h winds, dry
The overcast skies are a blessing. No direct sun means less heat stress on exposed ridgelines, while the cool overnight temperatures (8-10C) are manageable with proper layering during the 168K's night sections on Ucka. The lack of rain should keep the notoriously muddy forest trails relatively firm. These are conditions that favor fast times.
Inspiring Stories Beyond the Podium
Peter Macuh holds a unique distinction: he is the only athlete to have started the 100-mile race in every single edition since the event's creation. His loyalty to Istria 100 epitomizes the spirit of this race.
Eugen Kanjir, living with multiple sclerosis, will once again toe the start line, turning every step into an act of resilience. And 110K elite Genevieve Asselin-Demers balances athletic ambition, motherhood, and recovery from an epilepsy diagnosis as she takes on the Istrian trails this weekend.
How to Follow the Action
Live tracking and broadcasting will be available at live.utmb.world in English, French, and Croatian. The 168K runners depart from Labin at 17:00 CET on Friday, with the first finishers expected in Umag sometime Saturday morning. The full elite startlist is available on the official website.
And don't forget: this is a triple-header UTMB weekend. Check out our Desert Rats Trail Running Festival by UTMB preview for the full picture of this action-packed weekend on the UTMB World Series calendar.