We studied the cases of fifty-two patients with an infection at the site of a prosthetic total hip replacement, and are reporting the significant clinical features, infecting organisms, methods of treatment, and results at long-term follow-up. Forty-eight per cent of the hips had had an operation prior to the index arthroplasty, and 42 per cent had a wound complication. All patients had pain in the infected hip, but only 54 per cent had an erythrocyte sedimentation rate of more than thirty millimeters per hour, 44 per cent had fever, and 15 per cent had leukocytosis. In 88 per cent of the patients a single organism was grown on culture, and Staphylococcus epidermidis, Staphylococcus aureus, and Escherichia coli were present in about 75 per cent. When antibiotic therapy alone was the initial treatment, the infection was eradicated in only one patient. Excisional arthroplasty was the definitive surgical procedure in thirty-three patients and the infection was eradicated in twenty-seven of them, but the clinical result was satisfactory in only twenty. Of ten patients who had a true Girdlestone arthroplasty, none had recurrence of the infection and all had a clinically satisfactory outcome.