Objective: A systematic review of studies describing the course of functioning in patients with osteoarthritis (OA) of hip or knee, and identifying potential prognostic factors. Methods: A systematic search was carried out. Studies in patients with hip or knee OA, > 6 months follow-up and outcome measures on functional status or pain, were included. Methodological quality was assessed using a standardized set of 11 criteria and a qualitative data analysis was performed. Results: Approximately 6500 titles and abstracts were screened and 48 publications were considered for inclusion. Finally 18 studies, of which four met the criteria of high methodological quality, were included. In hip OA, limited evidence was established that functional status and pain do not change during the first three years of follow-up. After three years, however, a worsening of functional status and pain was seen. In knee OA, conflicting evidence was found for the first three years and limited evidence for worsening of pain and functional status after three years. Furthermore, limited evidence was established for negative associations between future functional status and laxity, proprioceptive inaccuracy, age, BMI, and knee pain intensity. Muscle strength, mental health, self-efficacy, social support and aerobic exercise, on the other hand, are protective factors in the first three years. Conclusion: Pain and functional status in hip or knee OA are slowly deteriorating, with evidence for worsening after three years of follow up. In specific subgroups, the prognosis is either worse or better as both risk factors and protective factors were identified. Prognostic factors included biomechanical factors, psychological factors, clinical factors and treatment modalities. To strengthen the evidence, however, there is a need for further high-quality prognostic research on functioning in hip or knee OA. (aut. ref.)