BACKGROUND: Medication non-adherence is prevalent in Parkinson's disease (PD) and results in substantial motor dysfunction. Although various approaches have been suggested to address non-adherence in PD, good quality evidence of associated factors is limited. OBJECTIVE: To systematically review the literature on clinical and demographic factors associated with medication non-adherence in PD. METHODS: We searched five online databases in April 2011 (updated in January 2012): MEDLINE, EMBASE, AMED, PsycINFO and CINAHL for studies reporting data on factors associated with medication non-adherence in people with idiopathic PD. Bibliographies were hand searched to acquire records not identified electronically. Two reviewers independently assessed identified articles for potential inclusion. Data extraction was undertaken using a standardised data extraction form. Methodological quality was assessed against a specially designed quality indicator tool emphasising the detection of threats to internal validity. RESULTS: We identified 1880 records of which six met inclusion criteria. A total of 772 PD patients were included (mean age 62 years, males 61%). We identified eleven factors (six clinical and five demographic) associated with non-adherence. We ranked each factor in order by weight of overall evidence: mood disorders, cognition, poor symptom control/QoL, younger age/longer disease duration, regimen complexity/polypharmacy, risk taking behaviours, poor knowledge of PD/education, lack of spouse/partner, low income, maintaining employment and gender. CONCLUSION: Clinicians should be aware of factors associated with medication non-adherence in PD. Targeted interventions should be developed and investigated to establish if addressing factors associated with non-adherence in PD leads to greater medication adherence.