The literature is devoid of complete descriptions of hip biomechanics during gait. We present for the first time simultaneously acquired in vivo acetabular contact pressures, ground reaction forces, kinematics, hip torques, and electromyographic (EMG) activity during gait with and without a cane from an 85-year-old male with a left instrumented femoral head prosthesis. Highest acetabular contact pressures occurred in all gait trials at the posterosuperior acetabulum, just prior to peak EMG, adductor torque, and ground reaction force during late stance phase. Contralateral cane use reduced both peak acetabular contact pressure and gluteus medius EMG but not adductor torque or ground reaction force. These data identify a small area of high acetabular and femoral head stress that could occur during each of a human's millions of gait cycles annually and indicate that muscle activity, rather than solely body weight, drives hip loading, Clinicians who desire to limit hip loads should reduce both hip muscle contraction and weight bearing in late stance.