Although osteoarthritis (OA) is the most common cause of articular skeletal disability in humans, assessing progression (staging) with noninvasive methods remains a major clinical problem. Using the rhesus macaque animal model, the objective of this study was to compare OA staging by noninvasive magnetic resonance imaging (MRI) against gross pathology and histopathology. Right knee joints from 18 rhesus macaques were used in this study. Using a four-point ordinal scale for each of the above-mentioned modalities, the lateral and medial femoral condyle and tibial plateau of each knee joint was independently scored for OA severity, i.e. normal, mild OA, moderate OA and severe OA. Correlation between each staging system was performed using Stuart's Tau-c correlation coefficient. By our criteria, MRI staging correlated as well with gross pathology (tau = 0.75) and histopathology (tau = 0.80) as did gross pathology with histopathology (tau = 0.78). Our study shows that MRI is a promising noninvasive modality to evaluate the severity of OA. MRI appears to be sensitive for demarcating the presence and extent of focal OA cartilage lesions. However, at this time, while MRI is sensitive for detecting OA change it cannot distinguish between certain lesions such as superficial cartilage matrix fibrillation and hypertrophy both of which show elevated signal intensity.