RESUMEN
Anastomoses between the median and ulnar nerves are commonly found on electrodiagnostic studies. These anastomoses are usually asymptomatic and are not discovered until nerve injuries occur that lead to unusual motor or sensory deficits. Their presence can cause difficulties in the interpretation of electrophysiological findings for the diagnosis of neuropathies and suppose a risk of iatrogenic damage during surgical procedures. We describe a rare case of bilateral Martin Gruber and Marinacci anastomosis, associated with median and ulnar nerve injuries in the carpal tunnel and Guyon's canal, respectively. The detailed anatomical knowledge of these anastomosis allows the electromyographist to identify them correctly, facilitating the interpretation of the findings and, incidentally, preventing iatrogenic injuries.