QUESTION:Does adding weekly, physiotherapist-delivered motivational interviewing to outpatient oncology rehabilitation for cancer survivors increase physical activity levels and improve physical and psychosocial outcomes that are typically impaired in this cohort? DESIGN:Randomised controlled trial with blinded outcome assessment, concealed allocation and intention-to-treat analysis. PARTICIPANTS:A heterogeneous sample of 46 cancer survivors (n=29 female; mean age 59 years) participating in a public outpatient oncology rehabilitation program. INTERVENTION:Participants were randomly allocated to receive oncology rehabilitation (n=24) or oncology rehabilitation with motivational interviewing delivered once weekly for 7 weeks via telephone by a physiotherapist (n=22). OUTCOME MEASURES:The primary outcome was amount of physical activity of at least moderate intensity completed in 10-minute bouts, measured by an accelerometer worn continuously for 1 week. Secondary outcomes included other measures of physical activity, sedentary behaviour, physical function, psychosocial function, and quality of life. RESULTS:When added to oncology rehabilitation, motivational interviewing caused no appreciable increase in the amount of moderate-intensity physical activity (MD -1.2 minutes/day, 95% CI -2.5 to 0.02). Among many secondary outcomes, the only statistically significant result was a small effect on nausea, which probably represents a Type I error. However, several secondary outcomes related to lower-intensity physical activity had non-significant confidence intervals that included large effects such as: sedentary time (SMD -0.67, 95% CI -1.32 to 0.02), light-intensity physical activity (SMD 0.56, 95% CI -0.12 to 1.21) and daily step count (SMD 0.37, 95% CI -0.30 to 1.02). CONCLUSION:Adding motivational interviewing to oncology rehabilitation did not increase moderate-intensity physical activity. Favourable trends on measures of lower-intensity physical activity suggest that motivational interviewing should be further investigated for its effects on reducing sedentary time and improving light-intensity physical activity for cancer survivors participating in rehabilitation. TRIAL REGISTRATION:ANZCTR 12616001079437. [Dennett AM, Shields N, Peiris CL, Prendergast LA, O'Halloran PD, Parente P, Taylor NF (2018) Motivational interviewing added to oncology rehabilitation did not improve moderate-intensity physical activity in cancer survivors: a randomised trial. Journal of Physiotherapy 64: 255-263].