A light microscopic, histochemical, and ultrastructural study was performed on tissue obtained from a pigmented squamous cell carcinoma of the cornea and conjunctiva. To the best of our knowledge this is the first time that one of these rare pigmented squamous cell carcinomas of the ocular mucous membrane has been described in detail. The occurrence of this neoplasm, which needs to be differentiated from other pigmented lesions, and particularly epibulbar melanomas, underscores the fact that all pigmented tumors are not melanomas. The study revealed that melanin granules, which accounted for the pigmentation of the neoplasm, were present in variable numbers in neoplastic squamous cells, Langerhans cells, macrophages, and stellate cells identified as melanocytes with mature melanosomes. Premelanosomes were not observed in any of these cells types. Current concepts concerning the common association of Langerhans cells with their characteristic intracytoplasmic "Birbeck granules" and melanocytes are discussed.