The work-of-fracture of human femoral bone was determined using the technique of Tattersal and Tappin (1966). The work required to fracture a specimen in three point bending by slow crack propagation through a triangular cross-section is obtained from the load-deflection curve. The area of the resulting fracture surface is measured by macrophotographic techniques, and the work-of-fracture is calculated as work per unit area. The work-of-fracture values measured in this way ranged from 3.8 to 11.8 (×10³) Jm⁻² in the samples tested with a mean of 7.8 × 10³ Jm⁻² and a standard deviation of 2.1 × 10−³ Jm⁻². The work-of-fracture was found to be independent of the degree of mineralization within the range of 60–80 weight %, and to not vary with transverse variation in location in the femoral shaft. The work-of-fracure was also seen to increase with increasing osteon fractional area. Scanning electron microscope photographs of the fracture surfaces indicate that the nature of the failure is similar to that of fiber reinforced composite materials.