Treatment of unreconstructible comminuted fractures of the radial head remains controversial. There is limited information on the outcome of management of these injuries with arthroplasty with a metal radial head implant. The functional outcomes of arthroplasties with a metal radial head implant for the treatment of twenty-five displaced, unreconstructible fractures of the radial head in twenty-four consecutive patients (mean age, fifty-four years) were evaluated at a mean of thirty-nine months (minimum, two years). There were ten Mason type-III and fifteen Mason-Johnston type-IV injuries. Two of these injuries were isolated, and twenty-three were associated with other elbow fractures and/or ligamentous injuries. At the time of follow-up, Short Form-36 (SF-36) summary scores suggested that overall health-related quality of life was within the normal range (physical component = 47 +/- 10, and mental component = 49 +/- 13). Other outcome scales indicated mild disability of the upper extremity (Disabilities of the Arm, Shoulder and Hand score = 17 +/- 19), wrist (Patient-Rated Wrist Evaluation score = 17 +/- 21 and Wrist Outcome Score = 60 +/- 10), and elbow (Mayo Elbow Performance Index = 80 +/- 16). According to the Mayo Elbow Performance Index, three results were graded as poor; five, as fair; and seventeen, as good or excellent. The poor and fair outcomes were associated with concomitant injury in two patients, a history of a psychiatric disorder in three, comorbidity in two, a Workers' Compensation claim in two, and litigation in one. Subjective patient satisfaction averaged 9.2 on a scale of 1 to 10. Elbow flexion of the injured extremity averaged 140 degrees +/- 9 degrees; extension, -8 degrees +/- 7 degrees; pronation, 78 degrees +/- 9 degrees; and supination, 68 degrees +/- 10 degrees. A significant loss of elbow flexion and extension and of forearm supination occurred in the affected extremity, which also had significantly less strength of isometric forearm pronation (17%) and supination (18%) as well as significantly less grip strength (p < 0.05). Asymptomatic bone lucencies surrounded the stem of the implant in seventeen of the twenty-five elbows. Valgus stability was restored, and proximal radial migration did not occur. Complications, all of which resolved, included one complex regional pain syndrome, one ulnar neuropathy, one posterior interosseous nerve palsy, one episode of elbow stiffness, and one wound infection. Patients treated with a metal radial head implant for a severely comminuted radial head fracture will have mild-to-moderate impairment of the physical capability of the elbow and wrist. At the time of short-term follow-up, arthroplasty with a metal radial head implant was found to have been a safe and effective treatment option for patients with an unreconstructible radial head fracture; however, long-term follow-up is still needed.