AimsThis systematic review aims to describe the dietary quality, dietary intake and related behaviours of adults diagnosed with cystic fibrosis.MethodsA comprehensive literature search was conducted in four databases (Medline, CINAHL, EMBASE, CENTRAL); studies were included if they addressed dietary intake, diet quality or eating behaviours among adults (≥15 years) living with cystic fibrosis and were published from January 2000 to November 2022. The Mixed Methods Appraisal Tool was used to assess the risk of bias and quality of included studies. Findings were synthesised narratively.ResultsNineteen observational studies (n = 2236) were included and considered high to moderate quality. Most (13/19) studies reported that individuals with cystic fibrosis were consuming high‐energy diets; where studies reported energy intake as a proportion of requirements met, energy intake was high, even when using individualised or cystic fibrosis‐specific referents. In addition, fat intakes as a proportion of energy appeared high (29%–39% of total energy), particularly as current guidelines recommend macronutrient profile similar to the general population (<30% of total energy). There was considerable variation in the reporting of fatty acid profiles and other nutrients. Five studies reported on concerns regarding diet and eating in this population.ConclusionFindings from the current review suggest dietary intakes of adults with cystic fibrosis appear to be less than optimal and concerns about diet, weight and food may be emerging in this population. Future research utilising consistent measures of dietary assessment and reporting, reporting of medical therapies, and exploring potential concerns about diet and eating is warranted.