OBJECTIVE To assess the intracompartmental pressure changes during the nailing of acute tibia fractures with the extrinsic factors of 90 degrees/90 degrees positioning, posterior thigh posts, continuous traction, and remaining removed. METHODS Prospective case control. METHODS Fifty-eight acute tibia fractures were nailed using an unreamed technique without leg elevation, thigh post, or continuous traction. Two presented with compartment syndrome and had fasciotomy before nailing. Thirty of the remaining fifty-six tibias had continuous intracompartmental pressure monitoring of the anterior compartment. RESULTS The highest pressures were routinely seen during manual reduction of the fracture (20-58mms Hg; avg = 34mm Hg) and during nail passage (15-56mms Hg; avg = 26mms Hg). In fifteen tibias, the pressure rose to within 30mmg Hg of the diastolic pressure and in 12 tibias the pressure exceeded 40mmg Hg. The pressures in all cases returned to baseline immediately following nail passage (avg = 13.8mms Hg). No sequelae of compartment syndrome was found in any of the 56 tibias presenting without compartment syndrome. There were no iatrogenic compartment syndromes in the series. CONCLUSIONS When extrinsic factors that increase intramedullary pressures are avoided, then intramedullary nailing raises the intramedullary pressure only momentarily. The pressure peaks during manual reduction and nail passage, and then returns to normal before the patient is awakened. Intramedullary nailing performed without reaming or traction is safe with respect to compartment syndromes and continuous pressure is not required.