OBJECTIVE The aim of this study was to delineate the results, mortality, and morbidity of partial lateral internal sphincterotomy for the treatment of chronic anal fissure. METHODS A retrospective review of 500 patients undergoing partial lateral internal sphincterotomy for chronic anal fissure between 1980 and 1990 was performed. Patients were identified by a review of an office surgical ledger and included all patients whose diagnosis was anal fissure and for whom a partial lateral internal sphincterotomy was performed as treatment. RESULTS Over an average follow-up of 5.6 years, only 1 percent of patients failed to health their fissures after performance of this operation. Minor complications included pain, pruritus, wound abscess, discharge, delayed healing, bleeding, fecal impaction, minor incontinence, and urgency and were present in 16 percent of patients, postoperatively. Two percent of patients who initially healed their fissures suffered a recurrence. Complication rates in open vs. closed sphincterotomy were 15 percent vs. 8 percent (P < 0.01). Disorders of fecal continence occurred in 8 percent of patients over the long term. CONCLUSIONS Extended follow-up after partial lateral internal sphincterotomy demonstrates a higher complication rate than was seen in patients being followed for shorter periods. However, the complication of impaired fecal continence only occurred in 8 percent of our patients, compared with 15 percent reported in the current literature, although using the same evaluative criteria. Patient satisfaction with the results of surgery was 98 percent. Careful patient selection, absence of preoperative continence problems, and meticulous surgical techniques are necessary to achieve this type of result.