Summary: We present the first case of cortical dysplasia with extensive intracerebral ossification. An eight-year-old epilepsy patient with a calcified lesion was successfully treated by surgical intervention. Pathological examination revealed a number of bizarre dysplastic cells in the whole lesion, which consisted of an epileptogenic cerebral cortex and a nonepileptogenic hamartomatous lesion with adipose tissue, vascular tissue, calcification, and ossification. The patient was diagnosed as having cortical dysplasia with ossification. Our findings support the notion that cortical dysplasia has a multipotentiality of cellular differentiation, including various hamartomatous tissues. We suggest that cortical dysplasia should be considered as a potential cause for epileptogenicity of a hamartomatous lesion even when magnetic resonance imaging (MRI) fails to disclose cortical dysplasia.