Lumbosacral plexus neuropathy (LSPN) is an idiopathic clinical syndrome characterized by the sudden onset of neuropathic pain, followed by weakness and sometimes sensory disturbances in the distribution of the lumbosacral plexus. Prognosis is usually favourable, although complete recovery may take several months to years. LSPN is the lumbosacral counterpart of the neuralgic amyotrophy syndrome (idiopathic brachial plexus neuropathy). We present a patient who initially was misdiagnosed with a radicular syndrome, but illustrates the typical signs and symptoms of LSPN. We also give clinical and electromyographical criteria for the diagnosis of LSPN and review the literature.