A previous report indicated that recreational runners had increased meniscal signal intensity and visible joint effusions on magnetic resonance (MR) images after jogging. Therefore, the knees of trained long-distance runners were evaluated by means of MR imaging before and after competition to determine the presence of any structural alterations, particularly changes in intrameniscal signal intensity and/or joint effusions. T1-weighted coronal, proton-density and T2-weighted sagittal, and short T1 inversion recovery sagittal images were obtained in five trained runners 24 hours before and within 24 hours after completion of a long-distance race (distance range, 17-50 miles). Pre- and postrace images were filmed and windowed with standardized techniques. All ligaments were normal before and after the race. No alteration in meniscal signal intensity was noted for any menisci, and there was no increase in joint fluid after running. These data indicate that the knees of trained long-distance runners do not demonstrate changes similar to those found in recreational runners, suggesting that these athletes may have adapted to the stresses of their activity.