544 women who had undergone voluntary tubal occlusion with Hulka-Clemens clips were reexamined 2-6 months after the procedure. 10 women were pregnant, or a sterilization failure of 1.83%. There were no ectopic pregnancies and failure of sterilization was clearly due in 6 cases to surgical error, in 3 cases to malfunction of the clip, and no reason was found for the remaining case. The operators had all been young doctors performing their 1st sterilization. According to the published literature, failure rates for female sterilization goes from 2-5.2/1000 for electrocoagulation, from 0.18% to 2-6/1000 with the Hulka clip, and it is about 0.33% with the Yoon ring. Causes for failure may be imperfect surgical equipment, procedure on a patient already pregnant, or surgical error. All surgical equipment must be carefully tested before all procedures, and young and yet unskilled operators must be checked during the procedure.