This study aimed to understand the processes of interpretation of, and responses to, the task of completing a theory of planned behaviour (TPB) questionnaire. Forty-five adults verbalized their thoughts while completing a full TPB questionnaire on walking behaviour. On average, participants' verbalizations indicated around 16 problems with the 52 questions. Further, problems as identified from verbalizations were associated with increased endorsement of the middle option on the questionnaire. Normative and intention questions were found to be particularly problematic. The current standardized method to develop TPB measures systematically yields problematic questions, as indicated by both talk and questionnaire responses.