Malignant peripheral nerve sheath tumors (MPNSTs) are very rare sarcomas derived from various cells in the peripheral nerve sheath. Malignant peripheral nerve sheath tumors have a known association with neurofibromatosis type 1. Diagnosis of MPNSTs is difficult in patients with chronic pain, when MPNST occurs at an overlapping area of chronic pain. Therefore, the diagnosis can be missed unless clinicians pay attention to the possibility of this disease. Here in, we report a case of concurrent malignant peripheral nerve sheath tumor with complex regional pain syndrome type 1. A 44-year female patient, who was diagnosed with complex regional pain syndrome (CRPS) type 1 in her left ankle, visited our clinic because of aggravated pain. The cause of the aggravated pain was revealed as concurrent MPNST in the left common peroneal nerve territory, which overlapped the site of pain from CRPS.