OBJECTIVE: As populations age and the prevalence of hip osteoarthritis (OA) increases, health care providers must manage increasing demands for services. Evidence regarding the progression of hip OA can assist health care practitioners in determining expected patient prognosis and planning care. This systematic review of prospective cohort studies examines prognostic variables in patients with hip OA. METHODS: Articles were selected following a comprehensive search of Medline, EMBase, CINAHL, and Allied and Complementary Medicine from database inception to October 2008 and hand searches of the reference lists of retrieved articles. Inclusion criteria involved 1) estimates of the association between prognostic variables and progression of OA, 2) prospective cohort design, 3) patients diagnosed with hip OA based on established criteria, 4) at least 1 year of followup, and 5) access to the full published text. Two independent reviewers assessed the methodologic quality of each study and the association between prognostic variables and OA progression. RESULTS: Eighteen articles met the inclusion criteria; 17 were considered to be of high quality. Strong evidence of progression was associated with age, joint space width at entry, femoral head migration, femoral osteophytes, bony sclerosis, Kellgren/Lawrence hip grade 3, baseline hip pain, and Lequesne index score > or =10. Strong evidence of no association with progression was associated with acetabular osteophytes. Evidence was weak or inconclusive regarding associations between various other radiographic or clinical variables, molecular biomarkers, or use of nonsteroidal inflammatory drugs. CONCLUSION: Overall, few variables were found to be strongly associated with the progression of hip OA, and a variety of other variables were weakly predictive of outcome.