Objective: The aim of this study, is to find out whether a myopathic involment accompanies muscle agenesis or not.Methods: Eleven patients were gathered in this study. The ages of cases were between 17 and 22 (mean: 19.9) years. Needle electromyography was performed in all patients. The serum CK and LDH values in the serum of all the patients were studied and in two cases muscle biopsies were taken from the unaffected side.Results: The electrophysiological findings in ten out of 11 patients with pectora|is major agenesis (six of them being very pronounced) were in accordance with myopathic involvement. In one case the histopathological examinations were in accordance with myopathic involvement, while there was not any pathological findings in the other one.Conclusion: As a result, we have concluded that a slowly progressive and benign myopathy may accompany muscle agenesis and this can be demonstrated by our electrophysiological investigations