We present the case of a patient with chronic low back pain with an unfavourable progression despite the prescribed pharmacological treatment. The patient had symptoms associated with compression of the sciatic nerve in an atypical area. As it passed through the piriformis muscle, it was diagnosed as piriformis muscle syndrome. This diagnosis was based on the clinical signs and symptoms and the determination of the tests performed, with the imaging tests being absolutely normal. Treatment is basically with non-steroidal anti-inflammatory drugs, muscle relaxants and stretching exercises of this muscle.