Histomorphometric changes in the trabecular structure of the principal compressive stress region in the femur in patients with osteoarthritis and fracture of the femoral neck are described. Femoral heads were obtained from patients who had surgery for the treatment of femoral neck fracture or total hip replacement for advanced osteoarthritis. Blocks from the principal compressive region of a coronal slice were sampled systematically to prepare 10 microns sections for automated analysis. There was no significant difference in the mineral bone content of the osteoarthritic (OA) and fractured neck of femur (FNOF) cases or between males and females for each group. The regression of mineralized bone on age was significant for OA data, showing a decrease in mineralized bone volume with age, whereas there was no significant relationship for the FNOF data. Surface density was significantly lower in the OA group than in the FNOF group despite the fact there is no difference in the mineralized bone. The regression of surface density on age was not statistically significant in both groups, although regression of surface density on the mineralized bone was significant for both groups and demonstrated that OA cases generated less surface than FNOF cases for the same amount of mineralized bone volume. The trabeculae in OA were significantly thicker than in FNOF, and spacing in OA was significantly greater than in FNOF. The regression of trabecular thickness and spacing on age was not significant for either OA or FNOF. For OA, thickness and spacing showed a significant regression on the mineralized bone volume, positive and negative, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)