Sir.—Chronic sinusitis associated with nasal polyposis is extremely common in patients with cystic fibrosis (CF), often necessitating frequent sinonasal surgery. The incidence of nasal polyposis in patients with CF is reported to range from 6% to 48%.1,2 The incidence of pansinusitis in children with CF has been reported to approach 100%.1,3,4 Although CF is usually diagnosed within the first 2 years of life, the diagnosis may be delayed until later childhood and adolescence or early adulthood in rare cases. Cystic fibrosis usually presents as recurrent bronchopulmonary infections and gastrointestinal malabsorption. However, sinonasal disease may be the initial presenting symptom. The prevalence of patients with CF presenting with sinonasal disease has not been reported. We describe three children with CF who presented with sinonasal symptoms. The diagnosis and management of sinus disease in patients with CF will be discussed, as well as the role of sweat testing in