We evaluated the occurrence of abnormalities in paranasal sinus radiographs in acute asthma by taking a radiograph of the sinuses of 110 consecutive patients admitted to a medical ward a total of 149 times for asthma. Maxillary sinus infection was assessed by taking aspirate from radiologically abnormal maxillary sinuses. An abnormal finding in any paranasal sinus was detected on 87% (130 of 149) of admissions and the yield of maxillary aspirate was macroscopically mucous, purulent or mucopurulent in 60% (42 of 70) of aspirates. A positive bacteriological culture was obtained from 23 aspirates and a virus was detected in 15, there being 7 aspirates in which both a bacterium and a virus could be detected. Although the correlation between radiographic findings and the aspirates was not very close we conclude that radiographic abnormalities of the paranasal sinuses are common in acute asthma as are infections of maxillary sinuses with an abnormal radiographic finding. There is an obvious need to look for sinusitis when a patient with an exacerbation of asthma is being evaluated.