Running speed decreases with increasing ambient temperature in both males and females. However, the decrease in running performance was shown to be lower in females than males at marathon distance (42.2 km) and 161 km ultramarathons. Nevertheless, the effect of ambient temperature on performance across shorter ultramarathon distances is unknown. Furthermore, except for morphological and physiological differences between males and females, it was suggested that the average speed of finishing females in higher ambient temperatures might be increased by slower females dropping out of the race. We aim to analyze the relationship between ambient temperature and average speed of males and females during shorter ultramarathon distances (50–100 km). We also aim to test the relationship between ambient temperature and the ratio of finishing females relative to males.