The objective of the study was to evaluate the factor of sex in terms of its influence on event-related potential components during the solution of a complex mental rotation task. To evaluate the factor of sex, independent of differences in ability levels and hormonal changes, women and men were equalized with respect to general intelligence and spatial ability. In addition, all women were tested during the low-estrogen phase of the menstrual cycle. The event-related potential analysis indicated that men showed shorter P3 and longer P1 latencies, as well as lower N1 amplitudes. These results suggest that men devoted more time to the analysis of irrelevant information presented in the rotation tasks, which resulted in mental rotation taking place earlier in men than in women. It can be concluded that, even though men and women showed similar performances on complex rotation tasks, they differed in their solution processes.