Stress urinary incontinence (SUI) is likelier to develop following a first pregnancy and delivery. Although retrospective epidemiological studies suggest an increased risk from both pregnancy and vaginal delivery, few cohort studies have estimated the long-term risk of SUI. This longitudinal cohort study examined the influence of SUI, beginning in a first pregnancy or puerperal period, on the risk of SUI symptoms 12 years later in 241 primiparous women entered consecutively into the trial in 1989 when seen for their first delivery. The 12-year incidence of SUI was based on 146 women lacking SUI for at least 3 months after delivery. By 12 years after the first delivery, 201 women had had 1-5 further pregnancies, and 187 had had 1-4 additional deliveries.The prevalence of SUI 12 years after the first delivery was 42%, and about 5% of women had SUI on a daily basis. Nearly 9% of women in the study reported hygienic problems or social discomfort resulting from SUI. The 12-year incidence of SUI was 30%. Any degree of SUI at 12 years was significantly more prevalent in women whose SUI began during the first pregnancy or within 3 months after giving birth, compared to women without SUI for at least the first 3 puerperal months. More than half of women whose SUI began during or after the first pregnancy but remitted by 3 months postpartum had SUI when assessed after 12 years. The risk of SUI 12 years after the first delivery was increased in women with higher body mass indices, but decreased in women who breast fed their infants for 6 months or longer and also in those having cesarean section at the first delivery. None of the women had undergone surgery for SUI. Training of the pelvic floor muscles did not lessen its prevalence.These findings show that, when SUI begins during the first pregnancy and especially the first delivery, the risk of symptoms 12 years later is significantly increased. Women who are obese before their first pregnancy and delivery appear to be especially at risk, whereas cesarean delivery may protect again long-lasting SUI in premenopausal women. GYNECOLOGYVolume 62, Number 5 OBSTETRICAL AND GYNECOLOGICAL SURVEY