In our retrospective study we compare the effectiveness and safety of transperitoneal laparoscopic versus open adrenalectomy in 40 patients with benign hyperfunctioning unilateral adrenal tumors. Patients 1 to 20 underwent open adrenalectomy between July 1988 and July 1992, and patients 21 to 40 underwent the laparoscopic procedure between September 1992 and January 1994. Student's t test for unpaired data was used to compare intraoperative and postoperative results, and morbidity observed in the 2 groups. The affected adrenal gland was successfully removed in all cases. Mean operative time was significantly longer for laparoscopy, although it shortened progressively due to the learning curve effect. Blood loss was significantly less with laparoscopy, while only 3 patients undergoing open surgery required blood transfusions. Overall invasiveness and analgesic requirement were significantly lower with laparoscopy. The intervals to oral intake and ambulation, hospital stay and return to preoperative normal activity were shorter with laparoscopy. Major complications were noted only in open surgery patients. At 3 months all patients in both groups were cured of the underlying adrenal disease. We conclude that transperitoneal laparoscopic adrenalectomy is equally effective and less invasive than open surgery, and that it should be considered the first choice therapy for benign hyperfunctioning adrenal tumors.