To summarize the current evidence on the effects of preoperative exercise therapy in patients awaiting invasive surgery on postoperative complication rate and length of hospital stay. A primary search of relevant key terms was conducted in the electronic databases of PubMed, EMBASE, PEDro and CINAHL. Studies were included if they were controlled trials evaluating the effects of preoperative exercise therapy on postoperative complication rate and length of hospital stay. The methodological quality of included studies was independently assessed by two reviewers using the PEDro scale. Statistical pooling was performed when studies were comparable in terms of patient population and outcome measures. Results were separately described if pooling was not possible. Twelve studies of patients undergoing joint replacement, cardiac or abdominal surgery were included. The PEDro scores ranged from 4 to 8 points. Preoperative exercise therapy consisting of inspiratory muscle training or exercise training prior to cardiac or abdominal surgery led to a shorter hospital stay and reduced postoperative complication rates. By contrast, length of hospital stay and complication rates of patients after joint replacement surgery were not significantly affected by preoperative exercise therapy consisting of strength and/or mobility training. Preoperative exercise therapy can be effective for reducing postoperative complication rates and length of hospital stay after cardiac or abdominal surgery. More research on the utility of preoperative exercise therapy and its long-term effects is needed as well as insight in the benefits of using risk models.