Istria 100 by UTMB

Istria 100 by UTMB crosses the Istrian peninsula in northwest Croatia from east to west, and every race finishes on the coast in Umag. The 168K leaves the old hill town of Labin at 5 p.m. on the Friday, climbs over Učka, the highest mountain in Istria, and comes down to Buzet before the long run west through the villages of the interior. It covers 168 km with 6,800 m of climbing on a 45-hour limit. The 110K and the 69K both start in Buzet on the Saturday morning.

Entry is first come, first served, opening to runners with a UTMB Index two days before everyone else, and the 168K and 110K both count as Western States 100 qualifiers.

The 168K runs from Labin over Učka to Buzet, where runners pick up their drop bags, then on through Butoniga, Livade, Grožnjan and Buje to Umag, with a cutoff at every checkpoint and the finish closing at 2 p.m. Sunday. The 110K starts in Buzet at 7 a.m. Saturday, climbs east to join the 168K course after about 20 km, comes back through Buzet and follows it to Umag, closing at 11 a.m. Sunday. The 69K leaves Buzet at 9 a.m. Saturday and takes the shortest line to Butoniga lake, then crosses the interior through Livade, Grožnjan and Buje to Umag, closing at midnight. The weekend's 42K from Motovun and 21K from Grožnjan are shorter than an ultra.

Registration for 2027 opened on June 16, 2026 for 48 hours to runners with a valid UTMB Index, then to everyone from June 18, and stays open until January 31, 2027 or until the races sell out, with no waiting list. Fees rise in tiers as places sell. A partial refund is available until February 1, 2027, and entries cannot be transferred to another runner.