The efficacy of a minimum dose of methylprednisolone for the prevention of posttraumatic hypoxaemia and fat embolism syndrome (FES) was prospectively studied in 87 patients with isolated, closed or grade I open, femoral and tibial fractures. On admission, the patients were randomly allocated either to a control group given placebo (40 patients) or to a methylprednisolone-treated group (47 patients). A total dose of 6 mg/kg BW methylprednisolone (SoluMedrol, Upjohn) was administered intravenously, divided in six equal doses at 8 h intervals. Six patients (12.8%) in the control group and one patient (2.5%) in the trial group developed FES (P = 0.079) but the difference is not statistically significant. Twenty-four hours after admission, the steroid-treated patients displayed statistically significant higher p(O2) values compared to the control group (P = 0.035) and this difference persisted on the second and the third post-admission day as well (P = 0.008). No corticosteroid-related side-effects were noticed in any of the patients during hospitalisation. Our results support the prophylactic administration of methylprednisolone in small dosage to prevent posttraumatic hypoxaemia and probably FES in patients with isolated lower limb long bone fractures, especially when early fracture stabilisation is not possible.