We treated 96 cases of pyogenic arthritis from January 1, 1980, to December 31, 1990, 16 of whom had adjacent osteomyelitis. Presenting symptoms in the latter were indistinguishable from those in 80 cases of primary pyogenic arthritis with regard to involved joints, aspirate findings and pathogens; however, adjacent osteomyelitis patients tended to be younger and were more likely to be symptomatic more than 7 days and to have received prior antibiotics. Prompt joint drainage was done in 15 of 16 cases but adjacent osteomyelitis was recognized in only 5. Bone scan was misleading in 3 of the 4 cases where it was performed as part of the initial evaluation. Persistent pain, swelling and/or fever occurred in 9 patients, 6 of whom underwent further joint drainage. Radiographs were diagnostic in 1 patient at admission, 10 during hospitalization and in 5 at follow-up. Sequelae were found in 8 of 13 patients with bone and joint infections vs. 8 of 41 patients with primary joint infection. Patients with a positive culture from the hip or shoulder who had been pretreated with antibiotics had the worst prognosis. Osteomyelitis should be considered in patients who present with symptoms and signs of pyogenic arthritis for longer than 1 week, especially if they have received prior antibiotics. Earlier recognition and bone debridement may improve outcome.