Introduction and Objective: Cystic fibrosis-related diabetes (CFRD) affects half of adults with CF. CFRD is associated with poorer outcomes. We estimate the longitudinal association between repeat measures of HbA1c and death in adults with CFRD in the UK. Methods: The UK CF Registry collects care and outcomes data with HbA1c measured in accredited NHS laboratories. We defined diabetes as documented diabetes; fasting plasma glucose ≥7 mmol/l or 2-hour value ≥11.1 mmol/l on oral glucose tolerance testing; or HbA1c ≥48 mmol/mol. Follow-up ran from an annual review with diabetes from 1 Jan 2013 to death or censoring as of 31 Dec 2022. We modelled HbA1c as a categorical time-dependent updated mean. To estimate mortality rates and magnitude of risk, we used Poisson regression and proportional hazards models controlling for age, sex, body mass index and pulmonary function (FEV1). Results: Among 5,630 people ≥18 years, 2,826 (50%) had CFRD and ≥1 HbA1c measurement. The mean age was 31 years, and updated mean HbA1c was 50.8 mmol/mol. Over 7.7 yrs (mean, SD 2.3) reflecting 21,835 person-yrs, 610 (22%) people died. Death rates rose with HbA1c (fig). Informed by guidance, compared to HbA1c ≤42 (mmol/mol), the hazard ratio for >42 to 53 was 1.5 (95% CI 1.1 - 1.9), for >53 to 69 was 2.0 (1.5 - 2.7) and for >69 was 2.3 (1.7 - 3.1). Conclusion: Glycemia is a modifiable risk for death. Since causes of death differ in CFRD from other types of diabetes, and few glycemic control trials exist, observational studies are key to informing care. Disclosure A.I. Adler: None. B. Shine: None. J.E. Snowball: None. S.C. Charman: None. Funding NIHR BRC