ABSTRACT Purpose Over the last decade, the number of prehabilitation randomised controlled trials (RCTs) increased drastically. This review aims to assess the reporting of sample size calculations in prehabilitation RCTs in cancer surgery patients. Methodology A comprehensive search was performed in multiple medical databases to identify RCTs evaluating the effectiveness of exercise, nutrition, and/or psychological interventions on postoperative outcomes of adult patients undergoing cancer surgery. Outcomes included type 1 error (α), power (1-β), mean (or mean difference between randomisation arms) and variance (e.g., standard deviation (SD)) for continuous outcomes, and event rates or event rate difference between randomisation arms. Using the information described in the published RCTs, an attempt was made to recalculate the sample size required, given a 10% margin of error using PASS 2023. Results Of the 60 included RCTs, 27 (45%) reported sufficient information to complete sample size recalculation. Of those that provided sufficient information, 11 (41%) provided variables that allowed for sample size replications within a 10% range of the reported sample size, whereas nine (33%) were >10% higher than reported sample size (max: 809% higher), and seven (26%) were >10% lower than reported sample size (max: 79% lower). Conclusions Over half of the prehabilitation RCTs exhibit poor sample size calculation reporting. More stringent reporting requirements are necessary.