Cerebral fat embolism (CFE) causes the neurological involvement observed in fat embolism syndrome, which is a post-traumatic complication seen mostly after long bone fractures and usually presents 24-72 h after the injury. An early 80s female who sustained an isolated traumatic fracture of the left distal femur without dislocation was alert on admission but fell into a coma 55 min after the injury. Brain computed tomography showed no abnormalities. Brain magnetic resonance imaging was performed approximately 5 h after the accident, and diffusion-weighted images revealed hyperintense, dot-like lesions disseminated in a "starfield" pattern in the brain. The patient was diagnosed with CFE and admitted to the intensive care unit. The day after the injury, the patient developed petechiae on the palpebral conjunctiva and was still comatose 4 months after the trauma. The current patient developing CFE in less than 1 h after a traumatic injury illustrates that CFE should be considered in patients with sudden deterioration of consciousness within 1 h after long bone fractures.