Severe cases of hidradenitis suppurativa affecting the perineum and gluteal regions may be treated successfully by 'deroofing' the sinus and fistulae tracts. These lie in the dermis and are partly epithelialized by cells from involved hair follicles and disrupted sweat glands. Careful preservation of the floor of the tracts leads to re-epithelialization with disease-free skin. More radical surgery is unnecessary and the problems of covering widely excised areas in this heavily contaminated region are avoided. By spreading the treatment over several operating sessions and hospital admissions, postoperative discomfort and in-patient nursing requirements are minimized. The technique of deroofing is described and the treatment of three severe cases is discussed. One patient illustrated the recognized complication of malignant change occurring in long-standing untreated disease. A fourth case illustrates the difficulties in diagnosing perianal hidradenitis suppurativa and literature cited suggests it to be a more common condition than once thought and a diagnosis frequently missed.