Several studies suggest that sex may affect cystic fibrosis (CF) disease severity, with females with CF being more severely affected. In this context, it has been suggested that sex hormones may influence the CF phenotype. A large proportion of females with CF regularly use oral contraceptives (OCs), but the effect of their use on disease severity is unclear. Here, we retrospectively assessed the effects of OCs on clinical outcomes in females with CF. Data from 681 females were available, of whom 42% had taken OCs for varying periods of time. We first performed an inter-patient analysis comparing annual change in % predicted forced expiratory volume in 1 s, body mass index and total days of intravenous antibiotic use over a 5-yr study period in 57 females exposed to and 57 females not exposed to OCs. There were no differences between the two groups. We next performed an intra-patient analysis of the same outcomes over a 3-yr period of OC exposure and a 3-yr period of no OC exposure in the same patient (exposure followed by non-exposure, n=27; non-exposure followed by exposure, n=23), but again did not detect any differences in any of the clinical outcomes. Our data suggests that the use of OCs does not affect CF disease severity.