Aim: Patient adherence is integral to the effectiveness of prescribed treatment, and is associated with beneficial disease outcomes, yet in adolescents with cystic fibrosis, adherence is often sub-optimal. Multiple factors may contribute to treatment adherence, including disease knowledge and self-efficacy. In adolescents with cystic fibrosis: (i) to compare the disease knowledge of adolescents and their parents before transition to adult care; (ii) to determine the relationship between disease knowledge (adolescent, parent) and adherence; and (iii) to evaluate self-efficacy and its association with disease knowledge and adherence. Methods: Adolescents with cystic fibrosis and their parents were recruited from a tertiary children's hospital. Disease knowledge and self-efficacy was assessed using the Knowledge of Disease Management-CF and General Self-Efficacy Scales respectively. Using pharmacy records, medication possession ratio was calculated to measure treatment adherence in the preceding year. Results: Thirty-nine adolescent (aged 12-17 (median 14) years) and parent pairs were recruited. Adherence to hypertonic saline, but not other medications, was significantly associated with disease knowledge in adolescents (r 2 =0.40, P=0.029). Mean (SD) adolescent self-efficacy was 30.8 (4.0), and not associated with disease knowledge or adherence. Mean (SD) disease knowledge was less in adolescents than parents (55 (16)% and 72 (14)% respectively, P<0.001). Conclusion: Disease knowledge is sub-optimal in adolescents with cystic fibrosis, even in the 2years immediately before transition to adult care. Given that adherence with some treatments has been associated with disease knowledge our results suggest the need for educational interventions in adolescents with cystic fibrosis to optimise self-management and health outcomes.