Twenty-one consecutive women with anal sphincter muscle rupture during delivery (0.79%) and 15 controls were examined. The anal sphincter was immediately repaired in the study group and the function determined with anal profilometry at 3 days and 3 months after delivery, and in ten of the patients after 12 months. Anal sphincter strength was reduced soon after delivery in the controls but regained normal strength within 3 months. In the anal sphincter rupture group, an improvement was found over the first 3 months after delivery, but afterwards no further change occurred. The anal sphincter strength was significantly reduced compared to the control group, both soon after delivery and after 3 months. Their voluntary anal pressure increased from 1.7 kPa immediately after delivery to 3.2 kPa at 3 months in the study group and the corresponding values in the control group were 4.0 and 6.5 kPa, respectively. For the closing pressure, that is the resting pressure minus the rectal pressure, the values in the study group were 4.2 and 6.7 kPa, and in the control group 7.2 and 9.4 kPa, respectively. In the women with anal sphincter rupture, however, a significantly increased frequency of gas incontinence was found.