Bone mineral density (BMD) and clinical status of 42 patients treated surgically 10-11 years earlier for an acute knee ligament injury were determined. The BMD was measured at the spine (L2-4) and the femoral neck, distal femur, patella, proximal tibia, and calcaneus of both lower extremities using dual-energy x-ray absorptiometric (DXA) scanner. The relative BMD results of the injured knee were correlated with sex, age, activity level, knee stability, and functional scores of the patient. In the 11 patients with moderate injury (isolated rupture of the medial collateral ligament), the BMDs of the injured and uninjured extremities were equal. In the 31 patients with severe injury (cruciate ligament rupture), the BMDs were significantly lower in the injured knee: distal femur, -6.0% (p = 0.0000); patella, -9.0% (p = 0.0000); and proximal tibia, -3.3% (p = 0.0012). Neither the femoral neck nor the calcaneus showed any differences. There were no significant differences either between men and women or between patients with different activity levels. The relative BMDs of the injured knee did not correlate with age or static knee stability but correlated significantly (r = 0.42-0.78, p < 0.01-0.001) with the functional scores of the same knee: the better the knee function in comparison with the healthy knee, the higher the relative BMD. The spinal BMDs corresponded with the age-adjusted reference values of the used densitometry. In conclusion, a severe knee ligament injury results in permanently decreased BMD in the injured knee. Other parts of the same extremity and lumbar spine are not affected.(ABSTRACT TRUNCATED AT 250 WORDS)