Insight into the causes of colorectal cancer (CRC) in adolescent and young adult (AYA) patients is limited. Without definitive information, patients often shape their own beliefs on the cause of their illness, developing causal attributions. This study aims to examine the causal attributions of CRC in AYA patients, compare these with middle-aged and older adults CRC patient groups and explore the association between causal attributions and psychological distress.Two cross-sectional questionnaire studies were conducted among CRC survivors diagnosed between 1998 and 2007 using the population-based PROFILES registry. Three groups were defined by age at diagnosis: AYA (18-39 years; n = 67), middle-aged (40-70 years; n = 1993) and older adult survivors (70+ years; n = 1922). Causal attributions were assessed in a single free-text item from the Brief Illness Perception Questionnaire and psychological distress measured by the Hospital Anxiety and Depression Scale.AYA survivors most often attributed their CRC to heredity (36.4%), lifestyle (14.5%) and chance (10.9%). AYA survivors attributed their CRC to these causes more frequently than middle-aged and older adult CRC survivors. AYA survivors who attributed their CRC to causes out of their control (chance, heredity) showed significantly lower mean scores on anxiety (4.3 vs. 5.6; p < 0.01) compared to AYAs who reported causes within their control (lifestyle, stress). No significant difference was found for depression.AYA patients with CRC may benefit from in-depth discussion about the lack of known (biological) causes and how this does not directly imply a lifestyle or stress cause.