PURPOSE: To correlate the pathologic and MR findings of distal femoral cortical irregularity(DFCI) in adult. MATERIALS AND METHODS: We retrospectively reviewed knee MR images of 120 adult patients(25-62 years old) without infection, tumor, or fracture. Five femoral specimens of adult cadaver were used to correlate pathologic and MR findings. A double cortical line' on MR images was interpreted as DFCI, and MR findings were analyzed to determine the thickness, internal signal intensity, location of the DFCI, shape of the external cortex, and clarity of the inner cortex. The outer cortex was classified as either convex or flat, and the inner cortex was classified according to its thickness and continuity as one of three types. RESULTS: One hundred and sixteen patients(97%) had DFCI, which in all cases was observed at the attachment site of the medial head of the gastrocnemius muscle. Mean thickness was 3.7mm and DFCI was thicker in men than in women(p<0.05). The outer cortex was convex in 75 cases(65 %) and flat in 41(35 %). The inner cortex was thick and continuous in 47cases(41 %, mean age 31), thin and continuous in 54(47 %, mean age 38), and thin and discontinuous in 19(16 %, mean age 47). Clarity tended to diminish with age. The internal area of DFCI showed signal intensity equal to that of adjacent bone marrow and was pathologically proven to be normal marrow tissue. CONCLUSION: DFCI was observed in most adults and was considered to be a normal variation. Its MR and pathologic findings were different to those observed during periods of growth.