Treatment of nasal polyposis with topical betamethasone is associated with suppression of the hypothalamo–pituitary–adrenal (HPA) axis and, potentially, has adverse effects on bone turnover. Fluticasone propionate is a potent corticosteroid with negligible absorption across the nasal mucosa and extensive first-pass hepatic metabolism. We performed a randomized double-blind study, in patients with nasal polyposis, comparing the effects of 8 weeks' treatment with betamethasone drops or fluticasone nasules on the HPA axis using the 1 µg tetracosactide test, and on bone turnover using two serum markers. Nine patients were allocated to each treatment. Betamethasone resulted in significant suppression in the tetracosactide test (P = 0.006), but fluticasone did not (P = 0.113). There were no differences in bone turnover or treatment efficacy between treatments. Treatment of nasal polyposis with topical betamethasone drops, but not with fluticasone nasules, suppresses the HPA axis and, given comparable efficacy, fluticasone administered via nasule should be the preferred agent.