This study evaluated forearm compartment pressures in 29 children with supracondylar humerus fractures. Pressures were measured before and after reduction in the dorsal, superficial volar, and deep volar compartments at the proximal 1/6th and proximal 1/3rd forearm. Pressures in the deep volar compartment were significantly elevated compared with pressures in other compartments. There were also significantly higher pressures closer to the elbow within each compartment. Fracture reduction did not have a consistent immediate effect on pressures. The effect of elbow flexion on post-reduction pressures was also evaluated; flexion beyond 90 degrees produced significant pressure elevation. We conclude that forearm pressures after supracondylar fracture are greatest in the deep volar compartment and closer to the fracture site. Pressures greater than 30 mm Hg may exist without clinical evidence of compartment syndrome. To avoid unnecessary elevation of pressures, elbows should not be immobilized in >90 degrees of flexion after these injuries.