AIM: Subjects who did not respond to an invitation to participate in a community-based randomised controlled trial for childhood obesity in Melbourne, Australia were approached to investigate reasons for non-participation. METHODS: Between January and September 2007, 305 families were sent a brief questionnaire and invited to take part in the current study. Thirty-seven questionnaires were returned and 12 parents agreed to a follow-up interview. Questionnaire data were quantitatively analysed. The interviews were conducted via the telephone and provided detailed qualitative information on non-participation. RESULTS: Lack of time was cited as a main reason for non-participation. Different aspects of time were discussed including lack of time to dedicate to a topic seen as low priority, overestimated perception of time for study commitments and the inappropriate timing of the request. Other major reasons for non-participation included risk of negative experiences and the impact of the initial contact with the study. CONCLUSIONS: This study illustrates the experiences of potential participants during the recruitment process, their perceptions of study commitments and how their previous experiences impact on their decision to participate in research. These findings provide insight into the decision not to participate in health research and could be used to modify recruitment procedures for future health research as a way of improving the recruitment experience for potential participants as well as enhancing recruitment rates.