A 57-year-old man presented with weakness in both legs upon awakening after drinking. Magnetic resonance imaging (MRI) of the lumbar spine did not reveal any intraspinal abnormalities but MRI of the pelvis revealed lesions with abnormal intensities with heterogeneous contrast enhancement in both gluteal muscles. Serum creatine phosphokinase was markedly elevated. A diagnosis of lumbosacral plexopathy, complicating rhabdomyolysis was made. With supportive care he recovered well but mild weakness of the right ankle remained at 6 month-follow-up. Pelvic MRI is a helpful diagnostic tool in localizing rhabdomyolysis. Lumbosacral plexopathy should be included in the differential diagnosis of the such cases, presenting with sudden weakness of legs.