Individuals high in alexithymia use high-risk sport to regulate their anxiety. Given the conceptual similarities between arduous high-risk sports and extreme endurance running, we investigated the relationship between alexithymia and the anxiolytic effects of endurance running. We measured marathon and ultramarathon runners (n = 35) on alexithymia, and pre- and post-race anxiety. Bootstrapped regression analyses using MEMORE revealed that alexithymia moderated the relationship between pre- and post-race anxiety such that there was a significant anxiety reduction for individuals high in alexithymia only. In conclusion, extreme endurance running provides an emotion regulation function for individuals high in alexithymia. The modest sample size points to the need for replication and further exploration.