An extended theory of planned behaviour including psychological distress was used to predict blood glucose monitoring in young adults with type 1 diabetes. Participants completed two surveys, a week apart (n = 167). Attitudes and perceived behavioural control were significantly associated with intention but subjective norm was not. Intention predicted blood glucose monitoring at T2. Higher scores in psychological distress significantly predicted poorer blood glucose monitoring at T2 but did not moderate the intention–behaviour relationship. Findings demonstrate some concerns with the theory of planned behaviour to predict self-care behaviour, yet highlight the importance of addressing psychological distress in diabetes self-management.