Hamartoma and choristoma are terms that describe non-neoplastic, mass-forming malformative lesions. Although each lesion has a different composition, they have been used interchangeably in many reports, especially for malformative lesions containing ectopic or heterologous elements. We report a three month-old girl who was brought to the clinic with a mass lesion at the posterior fontanel, composed of predominantly osteo-cartilaginous tissue admixed with skeletal muscle, peripheral nerve tissue, and ganglion. The mass was resected completely. The composition of this benign lesion with ectopic elements was consistent with an osteo-cartilaginous hamartoma. We discuss the biological and clinical aspects such malformative lesions within the skull to highlight the inconsistencies of the nomenclature used in the literature.