To review the effects of treating mild to moderate hypertension in women on mortality and cardiovascular morbidity and, further, to examine the evidence for the recommendation to treat women and men equally. A systematic step-by-step review of the literature up to May 2006 identified 80 randomized controlled studies of at least 6 months' duration; 67 were considered to be of satisfactory quality and were selected. Women were included in 59 of the 67 studies. The proportion of women increased from approximately 25% in 1975-1980 to about 40% in 2000-2005 (p < 0.05). Studies concerning hypertension and concomitant disorders often included fewer women. Results regarding blood pressure reduction were presented separately for women and men in 15 of the 59 studies with female participants, and most of these 15 studies showed no difference in mean blood pressure reduction between women and men. However, two large studies (ALLHAT and VALUE) demonstrated a greater reduction for women on calcium channel blockers. Outcome was reported separately for women and men in 33 studies, and in 28 of them, the outcome analysis was adjusted for sex by regression analysis or interaction by sex in multivariate analysis. No study had as the main objective to compare treatment effect between men and women. Direct scientific evidence from trials of antihypertensive treatment benefit specific to women is weak, but in studies where the analysis was adjusted for gender, the results appear to be similar for women and men. Future studies should be designed to study men and women separately.