A 60-year-old man developed two selective peripheral mononeuropathies of the peroneal and later the radial nerve, shortly after a diagnosis of large-cell lung carcinoma. Nerve conduction studies and electromyography confirmed isolated lesions in both nerves, and in the case of the peroneal nerve lesion, focal conduction block was localised to the level of the fibula neck. Subsequent magnetic resonance imaging of the lower limb excluded focal compression or malignant infiltration along the course of the peroneal nerve, and there was no signal change within the nerve, prompting a diagnosis of paraneoplastic mononeuritis multiplex. Anti-neuronal antibodies and serological markers of systemic vasculitis were negative. Neither the patient's large-cell lung carcinoma nor mononeuritis multiplex responded to chemotherapy, and he died within 6 months of the initial diagnosis.