We reviewed records of patients who underwent surgical treatment for anal fistulas arising from a chronic anal fissure. The subjects consisted of 26 patients (6 females, aged 27-74, median 44 years). We classified anal fistulas by Sumikoshi's classification. Three lesions were type I, 20 lesions were type II, one lesion was type III, and 2 lesions were other types. The laying-open method was performed in 21 patients and sphincter-preserving method in 4 patients. No recurrence was seen in any patients. We suggest that chronic anal fissures may progress in anal fistulas but surgical treatment is easy and safe in such cases.