Proliferative myositis (PM) is a rare benign soft tissue neoplasm with a distinctive pseudosarcomatous proliferative reaction of muscles in tumors. Its rapid growth and bizarre microscopic appearance often require a differential diagnosis from a sarcomatous lesion. It has been reported occasionally, mostly as case reports in adult patients. Herein, we present a neonatal case of PM. To the best of our knowledge, this is the first report in the neonatal period.