Gluteal compartment syndrome is a rare disorder which often occurs in conjunction with prolonged immobility after an overdose of sedative. Signs of sciatic nerve compression frequently occur, and rhabdomyolysis may be associated with the syndrome. We recently encountered a patient with lumbosacral plexopathy, complicated by gluteal compartment syndrome. A 42-year-old man presented with weakness and swelling in the right lower extremity and gluteal area after an overdose of antipsychotic drug, accompanied by prolonged immobilization. Serum creatine phosphokinase and urinary myoglobin were markedly elevated, and a T2-weighted pelvis MRI showed hyperintensities and swelling in the gluteal muscles. An electrodiagnosis study showed incomplete lumbosacral plexopathy. The patient received medical treatment and rehabilitation. Six months later, his right lower limb weakness had improved and he could walk independently. Lumbosacral plexus injury with rhabdomyolysis is a rare but debilitating disorder. Therefore, early diagnosis and treatment are crucial for prevention of neurologic deterioration.