The age at ovarian failure was determined in 90 women who had previously undergone abdominal hysterectomy with bilateral ovarian conservation and in 226 women who had undergone a spontaneous menopause. The mean age of ovarian failure in the hysterectomized group was 45.4 +/- 4.0 years (standard deviation), and this was significantly lower than the mean age of 49.5 +/- 4.04 years in the nonhysterectomized control group (P less than 0.001). There was a significant correlation between the age at hysterectomy and the age of ovarian failure in the women who were 44 years or less at the time of ovarian failure (r = 0.62, P less than 0.001), implying a causal relationship. The indication for hysterectomy did not influence the time of ovarian failure. Two explanations are proposed as to how conventional surgery for hysterectomy may adversely affect ovarian function.