Our goal was to produce a reliable, responsive instrument to quantify disease burden in children with acute sinusitis for use in clinical trials. In a cross sectional survey of 1611 community pediatric patients, parents rated the burden attributable to 13 sinus symptoms. Using logistic regression, we identified five symptoms that predicted the clinical diagnosis of sinusitis. The S5 is the average symptom score for nasal obstruction, daytime and nighttime coughing, headache and colored nasal discharge (range 0-3). The S5 was high in children with acute sinusitis (mean = 1.54, SD = 0.77, N = 93), and low in well children (mean = 0.42, SD = 0.56, N = 1019). We assessed reliability and responsiveness of S5 in a prospective cohort study of 41 children with sinusitis. Parents completed a questionnaire at the office visit, at 12 h and 3, 7, 10 and 14 days. Intra-subject reliability at 12 h was excellent (ICC = 0.94). The S5 score was responsive in 24 patients followed for 14 days who improved (mean change = 1.52, SD = 0.12, p = 0.0062). The S5 score is standardized, reliable, responsive, easily obtained, and can be used to determine study eligibility and assess treatment effects without a physician's evaluation.