Unrecognized sinusitis has been cited by others as a significant unrecognized factor in patients with asthma, chronic rhinitis, and urticaria. The current study examines the utility of roentgenography of the paranasal sinuses in such patients. Forty-seven percent of patients with flare-ups of asthma had abnormal sinus roentgenograms, a highly significant difference from the 29% prevalence in patients presenting with complaints of rhinitis. The patient's clinical history was most often not helpful in predicting whether or not roentgenographic abnormalities of the sinuses would be detected. Since maxillary sinusitis is the most frequent finding, the erect Waters' view is the most useful single roentgenogram.