This study aimed to investigate the diagnosis and consequences of pubic symphysis diastasis postpartum, in particular the use of ultrasonography to measure interpubic gap. It was a prospective follow-up study, which included an ultrasonographic comparison between symptomatic mothers and controls, set in Morriston Hospital, Swansea. Nine women presenting with unusual pubic pain post-partum were included: there were no exclusion criteria. Forty-two controls were also studied: the only exclusion criterion was unusual pubic pain. Interpubic gap was measured with ultrasonography. Follow up was undertaken for a median of 37 months (range 2-57). An abnormal interpubic gap was found in all symptomatic women. The incidence of diastasis was found to be at least one in 800 deliveries and significant long-term disability was found in three women. Diastasis is commoner than generally acknowledged and its consequences may be severe. Interpubic gap confirms diagnosis but does not appear to predict outcome. Ultrasonography aids diagnosis and follow up.