Introduction: The piriformis syndrome is known as an entrapment of the sciatic nerve, in which the pain is felt over the upper part of the buttock and radiates down the leg. However, the pain in the buttock may also be located in the area of the ischial tuberosity, accompanied by referred pain to the back of the thigh and this is called the hamstring syndrome. The reason for the piriformis syndrome is quite often hypertrophy or inßammation of the muscle and that condition can be caused by sport or other strain even straight injury to the piriformis muscle. The hamstring syndrome is very often a disease of athletes, especially of sprinters, but may also occur in non-athletes. The pain begins mostly without trauma. The symptoms of the hamstring syndrome are caused by the tense tendinous structures of the hamstring muscles. This tendinous structure presses the sciatic nerve when sitting or exercising. The treatment of these syndromes is always at þrst conservative but if the pain lasts long enough you must consider the operative treatment. Patients and methods: There were 75 patients in the years 1975–95 who were operated because of piriformis or hamstring syndrome (40 hamstring and 35 piriformis). We sent the questionnaire to the operated patients and 45 patients answered (23 hamstring and 22 piriformis). Our retrospective study group consists of 45 patients. There were 13 female and 9 male in the piri-formis group and 6 female and 17 male in the hamstring group. The average age was 45 years (ranged 28–66 y) in the piriformis group and 28 years (ranged 15–43) in the hamstring group. Results: The mean follow-up was 8 years (ranged 2–18 y). The most common symptoms before operation were radiating pain in thigh 20 in the piriformis and 18 in the hamstring sdr, pain in the buttock 17 and 21, pain in sitting 15 and 21. Typically many of the hamstring patients complained pain when stretching the leg. The patients had suffered the symptoms 5,6 years in the piriformis sdr and 1,6 years in the hamstring sdr average. The result of the operation was excellent or good according to patientsñ opinion in the18 (82%) piriformis and in the 18 (87%) hamstring syndromes. The common þndings in the operation in the piriformis sdr were tight and tendinous structure in piriformis muscle, n. ischiadicus and piri-formis muscle adhered to each other and thick piriformis muscle. In the hamstring sdr the þndings were one or more distinct tense tendinous structure like a violin string, n. ischiadicus adhered to m. biceps and adhesions to n. ischiadicus. Conclusions: We prefer conservative treatment at þrst, but if symptoms are difþcult and last many months so operative treatment is a good choice. The results were better in the hamstring sdr. A modiþed Kocher incision was mostly used. Of course the preoperative diagnosis must be correct and you must use all modern possibilities for good diagnosis for example MRI.