OBJECTIVE: To compare the effect of 2 oral contraceptives (OCs) on body weight. STUDY DESIGN: A randomized, parallel-group, multicenter study of 1,723 women taking an OC with norgestimate (NGM) 180/215/250 microg/ethinyl estradiol (EE) 25 microg vs. 1,171 women taking on OC with norethindrone acetate 1 mg/EE 20 microg for 6-13 cycles was performed. Body weight changes between baseline and cycle 6 and baseline and cycle 13 were analyzed. Analysis included not only changes in mean body weight but also the distribution of changes that were within 5% of baseline weight, 5-10% of baseline weight and > 10% of baseline weight. Only the 10% change was felt to be clinically significant. RESULTS: The distribution of body weight changes did not statistically differ between the 2 OC groups for any parameter measured. The mean weight change after 6 months for the NGM/EE and norethindrone acetate/EE groups was +0.71 kg and +0.57 kg, respectively. At 13 cycles for the NGM/EE and norethindrone acetate/ EE groups, the mean body weight change was +0.93 kg and +0.62 kg, respectively. Only 0.3% of subjects in both OC groups experienced a 10% change in weight. CONCLUSION: Use of OCs does not substantially affect body weight for most women.