Eighty-six children with chronic sinusitis, documented by x-ray with symptoms and signs for more than 12 weeks, were evaluated for atopy and B-cell immune abnormalities. Twenty-nine percent (25/86) of the patients had some B-cell abnormality of immunoglobulin isotype, IgG subclass, and/or hyporesponsiveness to pneumococcal polysaccharide (PPS) vaccine (Pneumovax). Eleven of 17 patients who were hyporesponsive to PPS vaccine had normal immunoglobulin isotypes and IgG subclasses. Twenty-six of these 86 children were followed prospectively for > or = 1 year on prophylactic antibiotics. The 12-month period before the use of prophylactic antibiotics was taken as the control period for each child for comparison. Nineteen of 26 (74%) children had a good outcome (greater than a 50% reduction in the number of exacerbations of sinusitis during a 12-month period compared with the previous year) on prophylactic antibiotics with a reduction in exacerbations of sinusitis from 9.8 per year to 2.7 episodes per year. In contrast, 7/26 had a poor outcome (p < .0001) on prophylactic antibiotics (from 12.6 per year to 8.7 per year on prophylactic antibiotics). There were no significant differences in age, gender, atopy, or presence of a B-cell immune abnormality in the good versus the poor outcome groups to prophylactic antibiotic therapy. Treatment outcome correlated inversely with the number of sinus infections before prophylactic antibiotics, p = .036. Underlying B-cell immune abnormalities could not be correlated with intervention outcome on prophylactic antibiotics. The use of prophylactic antibiotics was an effective treatment modality in children with chronic sinusitis, even in patients with selective immune abnormalities.