We review studies on the reliability of radiographic assessment of osteoarthritis of the hip and knee. Reliability studies were reported for 10 among 24 identified scores. In general, moderate to good agreement was found for overall scores and for separate grading of joint space narrowing of the hip and osteophytes of the knee in the majority of studies, while reliability tended to be lower for other radiographic features. Overall scores of the knee were more reliable than overall scores of the hip, and intra-rater-reliability was considerably higher than inter-rater-reliability in most instances. Comparison of reliability between scores can only be made with caution, given the difference in the design of reliability studies, particularly the different qualification of involved observers. The limits of existing knowledge on reliability of commonly used radiologic scores are outlined, and, proposals are made to overcome those limits in future studies.