The clinical characteristics of acute otitis media in relation to coexisting respiratory virus infection were studied in a 1-year prospective study of 363 children with acute otitis media. Respiratory viruses were detected using virus isolation and virus antigen detection in nasopharyngeal specimens of 42% of the patients at the time of diagnosis. Rhinovirus (24%) and respiratory syncytial virus (13%) were the two most common viruses detected. Adenovirus, parainfluenza viruses, and coronavirus OC43 were found less frequently. The mean duration of preceding symptoms was 5.9 days before the diagnosis of acute otitis media. Ninety-four percent of the children had symptoms of upper respiratory tract infection. Fever was reported in 55% and earache in 47% of cases. Patients with respiratory syncytial virus infection had fever, cough, and vomiting significantly more often than patients with rhinovirus infection or virus-negative patients. No significant differences were found in the appearance of the tympanic membrane and outcome of illness between virus-negative and virus-positive patients with acute otitis. Most patients respond well to antimicrobial therapy despite the coexisting viral infection. If the symptoms of infection persist, they can be due to the underlying viral infection, and viral diagnostics preferably with rapid methods may be clinically useful in these patients.