Cartilage degeneration in osteoarthrosis (OA) of the knee generally is believed to precede osseous abnormalities. Because cartilage abnormalities are not readily detected by routine radiography, we investigated the role of magnetic resonance imaging (MRI) in assessing cartilage damage in a goat model for OA. Four goats had the anterior cruciate ligament of one knee severed surgically to create instability and accelerate OA. Two goats each were killed at 4 and 6 weeks, respectively, after walking on the unstable knees. MRI of the knees was performed with Hybrid fat suppression sequences. The images were correlated with gross anatomic sections and histologic analysis of the knees. On gross examination, the unstable knees showed rapid development of thinning, surface irregularity, and focal defects of the cartilage. These findings correlated well with abnormalities detected on the MRIs. In addition, areas of decreased signal intensity in cartilage correlated with histologic evidence of degenerative changes in the cartilage substance, including fragmentation, fibrillary and eosinophilic changes, and chondrocyte proliferation, indicating attempted cartilage repair. Precise correlation of pathologic and MRI data, however, was lacking, related in part to inability to match perfectly the level and orientation of the gross section with that on the MRI examination.