Poor adherence to treatment can have negative effects on outcomes and healthcare cost. However, little is known about the barriers to treatment adherence within physiotherapy. The aim of this systematic review was to identify barriers to treatment adherence in patients typically managed in musculoskeletal physiotherapy outpatient settings and suggest strategies for reducing their impact. The review included twenty high quality studies investigating barriers to treatment adherence in musculoskeletal populations. There was strong evidence that poor treatment adherence was associated with low levels of physical activity at baseline or in previous weeks, low in-treatment adherence with exercise, low self-efficacy, depression, anxiety, helplessness, poor social support/activity, greater perceived number of barriers to exercise and increased pain levels during exercise. Strategies to overcome these barriers and improve adherence are considered. We found limited evidence for many factors and further high quality research is required to investigate the predictive validity of these potential barriers. Much of the available research has focussed on patient factors and additional research is required to investigate the barriers introduced by health professionals or health organisations, since these factors are also likely to influence patient adherence with treatment.