This study examined the prevalence of degenerative changes of knee menisci in aging and evaluated the diagnostic values of magnetic resonance (MR) imaging for assessing meniscal pathology in an older population. Eighty-five knees of asymptomatic volunteers over the age of 40 were scanned using MR imaging. Meniscal abnormalities were graded from 0 to 3 according to intrameniscal MR signals. The subjects were divided into two groups based on the presence or absence of radiographic osteoarthritis. Group I included 43 knees that had normal radiographs and group II consisted of 42 knees that had radiographic evidence of osteoarthritis. Degenerative changes in the menisci involved primarily the posterior segment of the medial meniscus in both groups. Signal changes in the other segments were of a significantly lesser grade than that in the posterior segment of the medial meniscus. The meniscal grade in each segment was significantly higher in group II than in group I. In group I, only two menisci (4.6% ) showed grade 3 signals, even in the posterior portion of the medial meniscus, compared to 21 (50.0%) in group II. Frequency of asymptomatic grade 3 was relatively low even in older subjects if there was no evidence of radiographic osteoarthritic changes. Abnormal MR signals are more likely to have clinical significance, in patients with radiographic changes on plain X-ray.