Studies of gender differences in the sexual activity of men and women after a first acute myocardial infarction (AMI) have produced conflicting results. The present study was performed to determine whether there are gender differences (1) in the quantity and quality of sexual activity after a first AMI, and (2) in the relations between selected demographic and medical variables and sexual activity after AMI. Four hundred sixty-two men and 51 women with a first AMI were interviewed once before discharge and again 3 to 6 months after AMI. Patients' demographic and medical background and their frequency of and satisfaction with sexual behavior were obtained from the interviews and from medical charts. Analyses of variance showed that women reported significantly less frequency of and satisfaction with sexual activity than men before and after AMI. Both women and men reported significantly less sexual activity and less satisfaction with sexual activity after AMI than before AMI. The decrease in frequency of and satisfaction with sexual activity after AMI was similar for women and men. The relations between selected demographic and medical variables such as age, education, and perceived health before the first AMI and the frequency of and satisfaction with sexual activity of the women and men did not appear to be affected differently by the AMI. A first AMI appears to reduce the frequency of and satisfaction with sexual activity of women and men similarly 3 to 6 months after AMI.