In speedboat racing in Japan, women racers participate and compete in races under the same conditions as men, and all individuals are randomly assigned to mixed-gender or single-gender groups for each race. In this paper we use a sample of over 140,000 observations of individual-level racing records provided by the Japanese Speedboat Racing Association to examine how male-dominated circumstances affect women's racing performance. We control for individual fixed-effects plus a host of other factors affecting performance (such as starting lane, fitness and weather conditions). Our estimates reveal that women's race-time is slower in mixed-gender races than in all-women races, whereas men racer's time is faster in mixed-gender races than men-only races. In mixed-gender races, male racers are found to be more 'aggressive' – as proxied by lane-changing – in spite of the risk of being penalized if they contravene the rules, whereas women follow less aggressive strategies. We find no difference in disqualifications between genders. We suggest that gender-differences in risk-attitudes and over-confidence may result in different responses to the competitive environment and penalties for rule-breaking, and that gender-identity also plays a role.