Background: Osteoma cutis, the presence of lamellar bone in the skin, is relatively common. This process is divided into two categories: primary osteoma cutis and secondary osteoma cutis. Objective: The purpose of this study was to describe the clinical and histopathologic features of patients in whom lamellar bone developed in cutaneous basal cell carcinoma. Methods: We evaluated the features of five cases of osteoma cutis associated with basal cell carcinoma and obtained detailed clinical information from those patients. Results: All five patients had significant underlying medical conditions, including two patients who were receiving interferon alfa-2b therapy. Three patients had been previously treated with electrodesiccation and curettage. The amount of sun exposure experienced by these patients varied. Histologically, the basal cell carcinomas were of the nodular or micronodular variety. Bone was found both in the stroma and intratumorally. Conclusion: The presence of bone within basal cell carcinomas is not uncommon and may be more prevalent in patients with an underlying medical disorder. (J Am Acad Dermatol 1998;38:906-10.)