Fifty-four children with acute mastoiditis were managed at the Los Angeles County-University of Southern California Medical Center from 1972 through 1982. Our criteria for the diagnosis of acute mastoiditis are acute or subacute otitis media, postauricular swelling and erythema, protrusion of the auricle, and clouding of mastoid air cells on radiographs. Thirty-one (57%) recovered with conservative therapy consisting of early myringotomy and intravenous antibiotic, usually ampicillin. Twenty-three patients were managed surgically. The indication for surgery in each case was the clinical diagnosis of subperiosteal abscess; mastoid radiographs played no part in the decision to operate. Two of the 23 patients managed surgically had only incision and drainage of abscess; simple mastoidectomy was performed on 20 and radical mastoidectomy on one. Etiologic bacteria were cultured in 21 instances, S. pyogenes was cultured in 9, S. pneumoniae was cultured in 6, H. influenzae in 1, enterococci in 1, anaerobes in 2, and M. tuberculosis in 2.