One hundred consecutive cases of trauma with associated fractures of the lower limb long bones were studied for the subsequent development of the fat embolism syndrome (FES). This is to be differentiated from the intravascular fat embolism which often occurs without clinical FES becoming manifest. Seventeen of the patients developed the clinical picture, with a further 16 patients being considered to have had the syndrome subclinically. Clinical and biochemical features were studied to determine pointers to the early diagnosis and patient "at risk" of developing FES. Young males under the age of 30 with significant hypoxemia occurring early in the course of the disease were considered the most likely candidates "at risk" for developing FES. These results favor the concept that FES is essentially a form of respiratory insufficiency syndrome similar to that which occurs following trauma in other situations, e.g., shock lung.