If the right hemisphere is dominant for activation and this capacity is critical for normal sexual function, one might expect to find a greater incidence of impaired sexual function after right than after left hemisphere stroke. We found that the prevalence of major sexual dysfunction was significantly greater after right (9/12) than after left (4/14) hemisphere stroke in 26 men with unilateral stroke. These data are consistent with the hypothesis that activation is critical for sexual function as well as the hypothesis that the right hemisphere is dominant for sexual function. © 1986, American Medical Association. All rights reserved.