A review of thirty-eight patients with Kienböck's disease indicated that both delay in diagnosis and prolonged treatment by plaster immobilization led to progressive collapse of the lunate and an unsatisfactory result in most instances. Four clinical and roentgenographic stages were identified, and the results of silicone replacement arthroplasty were correlated with the preoperative stage after an average follow-up of twenty-seven months. The results were satisfactory in fourteen of twenty wrists in which the procedure was performed before collapse of the lunate had occurred. The importance of early diagnosis and early surgical treatment of this disorder was emphasized by the findings in this study.