Hysterosalpingography (HSG), performed in the first 3 months after tubal ligation, has demonstrated a 1% to 2% incidence of tubal patency when initial operative errors have been excluded. In a group of 54 women, HSG was performed a mean of 4.8 years following sterilization; 9 women (16.7%) demonstrated spillage which was confirmed at laparoscopy in 7 of 8 women operated upon. No cases were due to initial surgical error. Delayed acquisition of tubal patency may explain late failure of tubal ligation, and the abnormal tubal lumen formed may be responsible for the increased percentage of ectopic pregnancies observed among sterilization failures. Ectopic pregnancy must be strongly considered in any failure of tubal ligation. In investigating the proximal tubal segment prior to consideration for tubal reconstruction, the possibility of a pre-existing or an iatrogenically formed fistula must be recalled which may predispose the patient to ectopic pregnancy.