The metabolic cost of walking and jogging following injury to the anterior cruciate ligament is unknown. Economy of motion refers to the oxygen consumption for a submaximal work rate. The purpose of this study was to compare the economy of walking and jogging of an anterior cruciate ligament-deficient population with that of a control population without orthopaedic abnormalities. Steady-state oxygen consumption was measured in 30 patients and 98 controls while they were on a treadmill at various speeds. Deficiency of the anterior cruciate ligament was diagnosed arthroscopically. The patients also were tested for isokinetic knee extension-flexion strength, hip flexion, and abduction and adduction strength and underwent arthrometric measurement of anterior tibial displacement. The patients had a statistically significant increase in oxygen consumption when jogging at 160.9 m/min (p = 0.007); however, there was no significant effect of anterior cruciate ligament deficiency on economy at the other speeds tested. The patients had significant deficits in strength of all muscle groups tested. Steady-state oxygen consumption at 160.9 m/min tended to be inversely related to the deficit of strength of knee flexion (r = -0.44, p = 0.07). Arthrometric measurements and chronicity of injury were unrelated to steady-state oxygen consumption. These data indicate that anterior cruciate ligament deficiency increases oxygen consumption during jogging. In long-distance running, this decreased economy translates into significant additional caloric requirements, which may result in earlier fatigue.