Objective: To determine whether the presence of opacification in the paranasal sinuses of children and adolescents without rhinosinusitis implies an increased risk of later development of upper respiratory tract symptoms. Methods: This was a prospective study of a cohort of patients aged 0 to 18 years who underwent computerized tomography (CT) scans for indications unrelated to rhinosinusitis. Sinus opacification was evaluated using an opacification/development ratio score. The patients' clinical progression was followed up using a questionnaire for 1 month after the scans. Results: Fifty-six percent (56%) of the 106 patients enrolled in the study had opacity, the majority due to mucosal thickening. Intense opacification was defined as "suspected" (score >= 15) and patients in this subset had a greater risk of developing symptoms during follow-up (odds ratio = 2.74; 95% CI 1.10-6.83) compared to those with no findings or discrete findings. Conclusions: Intense incidental sinus opacity on CT indicates a risk of future development of a clinical respiratory condition.875433438