Nineteen patients with 20 severe proximal humeral fractures were treated early with a Neer humeral prosthesis from 1979 to 1986. There were 18 four-part and two three-part fractures. The average age of the patients at the time of injury was 64 years. Follow-up evaluation was performed at an average of 40 months. Pain relief was satisfactory in 18 of 20 fractures. Patients were satisfied with the result in 16 of the 20 shoulders. Functional evaluation was good or fair in 15 of 20 patients. Active forward elevation averaged 72 degrees and active external rotation 16 degrees. Complications consisted of one axillary nerve palsy, one postoperative posterior dislocation, loosening of one uncemented humeral prosthesis, and one breakage of fixation wire requiring subsequent removal. Patients who could not comply with the postoperative rehabilitation program had poor results. Poor function appeared to be directly related to lack of rotator cuff integrity. Surgical techniques designed to securing tuberosity union are essential.