The aim of this study is to investigate the results of open lateral internal sphincterotomy (LIS) and the recurrence and incontinence rate, to perform a long-term assessment of incontinence and to assess complications and relief of symptoms. This clinical prospective study was undertaken in patients undergoing open LIS. One hundred and twenty-nine patients entered the study. Mean duration of pain relief was 1.2 +/- 0.4 days and mean time before defecation without pain was 1.9 +/- 1.0 days. Complication rate was 41.8%. We found that urine retention was seen frequently in males. We demonstrated that open LIS up to the dentate line does not have a higher rate of incontinence. Incontinence after LIS was only to flatus and two-thirds of these resolved in 6 weeks. No patient showed improvement of incontinence after 6 weeks.