The purpose of this study is to estimate the age of cadavers by histomorphometry of the femur. Seventy-two Japanese males ranged from 43 days to 92 years old and 26 females ranged from 2 to 88 years old were used. The thickness of sections was adjusted at 50 to 70 microns by grinding with sand paper. The sections were not decalcificated. They were stained with Villanueva's bone staining powder and with thionin dye. Microradiographs of the sections were obtained by the soft X-ray apparatus. The area, maximum and minimum diameter, and perimeter of the perfect osteon and Haversian canal were measured. In addition, the type II osteon number, osteon fragment number, and area of triangle were also determined. All these parameters were examined by an image analyzer. The parameters of the osteon showed high correlation coefficient with age (magnitude of r > 0.77), while those of the Haversian canal were low (magnitude of r < 0.11). All parameters were subjected to multiple regression analysis for producing a multiple regression equation of age estimation. For the stepwise selecting method, the perimeter of osteon, maximum length of the Haversian canal and osteon fragment number were selected for the equation. Their multiple r2 and standard error of estimation were 0.8874 and 6.39, respectively. For the forward selection method, in addition to the above items, three parameters, the maximum length of Haversian canal, triangle area, osteon fragment number were selected. Their multiple r2 and standard error of estimation were 0.9484 and 4.884, respectively. Bone staining was useful to clarify the demarcation between osteon and fragment, leading to an increase in the accuracy of age estimation. However, the entire range from birth to 90 years was difficult to cover for precise age estimation.