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?Randomised controlled trial with blinded outcome assessment, concealed allocation and intention-to-treat analysis.A heterogeneous sample of 46 cancer survivors (n=29 female; mean age 59 years) participating in a public outpatient oncology rehabilitation program.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).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.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).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.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].