In a consecutive series of 274 patients with isolated femoral shaft fractures 11 patients (4%) developed fat embolism syndrome. There were no cases of fat embolism syndrome in patients over the age of 35 years. Of the remaining patients, 60 operated on within 10 h of injury did not develop fat embolism. This left 109 patients who had nailing performed more than 10 h after injury of whom eleven (10%) developed fat embolism syndrome (p < 0.027). Patients under the age of 35 years with isolated femoral fractures should have nailing performed as early as possible after injury to minimize fat embolism syndrome.