Results: We identified 32 trials published in 45 papers. Only 16 (50%) trials were registered, withall 16 trials being completed and published. Of the unregistered trials, we identified three (19%)for which similarities in the sample size and participant demographics across papers was sug-gestive of duplicate publication. Identification of potential duplicate publications was difficultfor the remaining 13 (81%). Results from 53 (76%) of the 70 registered outcomes were published,but 11 (69%) registered trials reported results from additional outcomes not prospectively regis-tered. A total of 46 different outcomes (out of 53 reported outcome measures, similar measureswere collated) were reported across all trials, 31 (67%) of which were collected in ≤2 trials.Conclusions: We found direct evidence of trial registration issues in experimental trials of break-ing up sitting-time. The lack of prospective registration of all trials, and the large number ofoutcomes measured per trial are key considerations for future research in this field. Theseissues are unlikely to be confined to the field of sedentary behaviour research.