Mesenchymal chest wall hamartoma is an extremely rare tumor striking neonates and infants. Histologically, the tumor is composed of islands of hyaline cartilage intermixed with mesenchymal-like stroma and hemorrhagic cysts. We present a case of a congenital bilateral mesenchymal chest wall hamartoma (MCWH) in an infant boy. This extremely rare benign entity may be misdiagnosed as malignant tumor and shares features with another tumor of childhoodfibrocartilagenous mesenchymoma of bone. Copyright © Informa Healthcare USA, Inc.