Fifty patients receiving estradiol implants for long-term treatment of premenstrual syndrome were studied over 5.6 years (range 2-8 years). There was a continued beneficial response to treatment in all symptoms, varying between 74% for bloating and 96% for depression. Menstrual cycle control improved in 31 patients and periods were less painful in 30 patients. Cyclical progestogenic symptoms occurred in 58% of patients. These were partially relieved by alterations in dose, type and duration of progestogen treatment but in 7 patients the symptoms remained severe. Eight patients had a hysterectomy during treatment; 5 for continuing progestogenic symptoms, 1 for prolapse and 2 for prolonged menstrual bleeding despite adequate progestogen therapy. Attempts to reduce the dose of progestogen led to cystic hyperplasia in 4 patients. This was treated by hysterectomy in 2 patients and corrected with two 21-day courses of progestogen in the other 2. Uterine enlargement with a mean weight of 133 g (125-145 g) associated with myometrial hypertrophy occurred in all 8 hysterectomy patients. There were no complications form venous thrombosis, pulmonary embolus, breast disease or atypical endometrial hyperplasia.