Purpose: Strength athletes often employ the deadlift in their training or rehabilitation regimens. The purpose of this study was to quantify kinematic and kinetic parameters by employing a three-dimensional analysis during sumo and conventional style deadlifts. Methods: Two 60-Hz video cameras recorded 12 sumo and 12 conventional style lifters during a national powerlifting championship. Parameters were quantified at barbell liftoff (LO), at the instant the barbell passed the knees (KP), and at lift completion. Unpaired t-tests (P < 0.05) were used to compare all parameters. Results: At LO and KP, thigh position was 11-16°more horizontal for the sumo group, whereas the knees and hips extended approximately 12°more for the conventional group. The sumo group had 5-10°greater vertical trunk and thigh positions, employed a wider stance (70 ± 11 cm vs 32 ± 8 cm), turned their feet out more (42 ± 8°vs 14 ± 6°), and gripped the bar with their hands closer together (47 ± 4 cm vs 55 ± 10 cm). Vertical bar distance, mechanical work, and predicted energy expenditure were approximately 25-40% greater in the conventional group. Hip extensor, knee extensor, and ankle dorsiflexor moments were generated for the sumo group, whereas hip extensor, knee extensor, knee flexor, and ankle plantar flexor moments were generated for the conventional group. Ankle and knee moments and moment arms were significantly different between the sumo and conventional groups, whereas hip moments and moments arms did not show any significantly differences. Three- dimensional calculations were more accurate and significantly different than two-dimensional calculations, especially for the sumo deadlift. Conclusions: Biomechanical differences between sumo and conventional deadlifts result from technique variations between these exercises. Understanding these differences will aid the strength coach or rehabilitation specialist in determining which deadlift style an athlete or patient should employ.