The aim of this study was to evaluate the effect of postpartum pelvic floor muscle exercise in the prevention and treatment of urinary incontinence. A prospective comparison design of 99 matched pairs (n= 198) of mothers, a training group and a control group, was used. Eight weeks postpartum the training group attended an 8-week intensive pelvic floor muscle exercise course, training in groups led by a physical therapist for 45 minutes once a week. In addition they were asked to exercise at home at least three times per week. The control group followed the ordinary written postpartum instructions from the hospital. Pelvic floor muscle strength was measured pretreatment at the eighth, and post-treatment at the 16th week after delivery, using a vaginal balloon catheter connected to a pressure transducer. Vaginal palpation and observation of inward movement of the balloon catheter during contraction were used to test the ability to perform correct the pelvic floor muscle contraction. Urinary leakage was registered by interview, specially designed instruments to measure how women perceive SUI, and a standardized pad test. At baseline (8 weeks postpartum) there was no significant difference in the number of women with urinary incontinence in the training group compared to the control group. At 16 weeks postpartum, after the 8-week treatment period, there was a significant (P<0.01) difference in favor of the training group. In addition, a significantly greater improvement in pelvic floor muscle strength between test 1 and test 2 was found in the training group compared to the control group. The results show that a specially designed postpartum pelvic floor muscle exercise course is effective in increasing pelvic floor muscle strength and reducing urinary incontinence in the immediate postpartum period.