Introduction Studies have reported circadian desynchronizations and sleep disruptions in onshore populations in the Arctic during the polar day. Although the Arctic region is becoming more accessible by sea and evidence is growing to implicate the importance of fatigue in sailing accidents, no study related to circadian disruptions has focused on sailors. The aim of this study was to observe, during a 155-d polar sailing trip between Greenland and Russia, the evolution of the sleep-wake rhythm and core body temperature (Tc) in a sailor. Methods During the expedition, an electronic sleep diary was recorded daily and a continuous measurement of Tc using telemetric pills was performed every 10 d (recording depending on transit time, ≈24 h). Ephemerides were manually determined day by day using global positioning system position and revealed 3 phases (phase 1: decrease of night duration; phase 2: polar day; phase 3: increase of night duration). Results A significant difference (P<0.05) was observed in daily sleep time between phase 2 (7.6±2.5 h) and phase 3 (8±2 h). The period of Tc rhythm changed during the expedition (phase 1: 24.2±0.5 h; phase 2: 25±0.3 h; phase 3: 24±0.6 h). Dissociation between Tc rhythm and sleep occurred during phase 2. Conclusions Our study observed that during a polar sailing expedition, many circadian disruptions appeared as free-running rhythms or dissociation between sleep and Tc rhythm. Future studies will evaluate effects of these disruptions and their probable association with accident risks.