Signs, symptoms, and radiographic abnormalities of sinusitis are frequent in children with asthma; it is not known whether sinus inflammation is associated with bacterial infection or other mechanisms. Eight asthmatic patients with exacerbation of asthma despite bronchodilator therapy were studied after maxillary sinusitis was confirmed by radiographs. All had cough, wheezing, nasal stuffiness, rhinorrhea and were afebrile. Four patients had headaches, and two had facial pain. Maxillary sinus aspirates were obtained, and bacterial cultures were positive in five: Branhamella catarrhalis (2), nontypeable Hemophilus influenzae (2), Streptococcus pneumoniae (1). Nose and throat cultures did not correlate with sinus cultures. All patients received bronchodilators, and four of eight patients received steroids. All were treated for 14 to 28 days with antibiotics during which seven of the eight patients improved clinically including all with positive sinus cultures. Asthma-symptoms diary scores were kept by five; all demonstrated improvement. Pulmonary-function tests improved in five of seven patients after the antibiotic and asthma therapy including the four patients with positive cultures. Sinus radiographs cleared in three, improved in three, and were unchanged in two patients after antibiotic therapy.