Sleep disturbance has been described in cystic fibrosis (CF) patients as relevant to clinical and lung function predictive factors helping to improve the diagnosis and early intervention. Related paediatric studies are scarce. Objective: To describe respiratory sleep disturbance (RSD) and its association with spirometric indices in a population of CF children. A second aim was to determine if spirometric indices and wake-time SpO2 are predictors of sleep disturbance. Methods: A cross-sectional study involving 33CF paediatric patients. All participants underwent in-lab polysomnography (PSG), pulse oximetry and spirometry. A standardized sleep questionnaire was completed for each patient. Two subgroups were considered: I – Normal (FEV1 > −1.64 z-score); II – Obstructed (FEV1 ≤ −1.64 z-score). Results: Participant's median age was 12 (6–18) years, 16 (48.5%) were male. Twenty-nine patients (87.9%) presented sleep complaints. Sleep efficiency was reduced; sleep latency and waking after sleep onset (WASO) increased. N1 increased, N2, N3, REM and awakenings were normal. The apnoea–hypopnoea index was 0.6/h (sd 0.9); respiratory disturbance index (RDI) was 6.6/h (sd 5.2). Mean awaking (97% (sd 1.1)) and sleep SpO2 (95% (sd 2.7)) were normal; mean nocturnal oximetry desaturation index was 2.36/h; minimal nocturnal SpO2 was 89% (sd 4.1).We found associations between mean nocturnal SPO2 and mean values of FEV1 (r = 0.528; p = 0.002) and FEF25–75 (r = 0.426; p = 0.013). There were significant differences in nocturnal SpO2 between normal and obstructed patients (p < 0.000). PSG data correlated with the questionnaire answers for night awakenings and WASO (p = 0.985) and difficult breathing during sleep and RDI (p = 0.722).This study points to most CF children having sleep complaints, and highlights the correlation between subjective assessment of sleep and PSG and spirometric results. Awake-time SpO2 and spirometric values are possible risk predictors for nocturnal desaturation. Keywords: Sleep disturbance, Polysomnography, Spirometry, Cystic fibrosis, Children