Background: Although socioeconomic status (SES) can impact the outcomes of people with cystic fibrosis (CF), little is known about the relationship between parental SES and lung function in their offspring with CF. Aim and Objectives: To investigate the association between parental SES and lung function in offspring with CF. Method: This register-based study includes study individuals with a diagnosis of CF born in Sweden 1973-2019 identified using the national Swedish CF Registry, from which yearly lung function measurements (FEV1 and FVC) from 5 to 25 years of age were also retrieved. Data on parental SES (education and disposable income at birth of offspring) was retrieved from Statistics Sweden. The relationship between parental SES and lung function was studied using linear mixed models adjusted for potential confounders retrieved from national health and demographic registers. Results: In total 650 individuals with CF were identified. Distribution of SES among mothers showed 15.7% in lowest education group (compulsory school only) and 18.8% in lowest income group, similar for fathers. No association was found for the comparison between the lowest and the highest group for maternal education and offspring FEV1 z-score (? -0.03, 95% CI -0.07, 0.00) or maternal income and FEV1 z-score (? -0.02, 95% CI -0.06, 0.03). No association was found for maternal education and FVC z-score (? -0.00, 95% CI -0.04, 0.03) or maternal income and FVC z-score (? 0.02, 95% CI -0.04, 0.07). Findings for fathers was similar. Conclusion: No association was found between parental SES and lung function in offspring with CF and this should be explored in other healthcare settings.