Goblet cell carcinoid (GCC) is a rare but distinctive neoplasm with features of both adenocarcinoma and carcinoid tumor. Most cases described in the literature have occurred in the appendix. An additional well-defined location is the ovary, and these tumors have been associated with a mature teratoma of the ovary. GCC arising within a mature teratoma of the mediastinum has not been described in the English-language literature. We report a case of this previously undescribed entity and provide a review of the literature on mediastinal teratomas with malignant transformation. The histologic findings included uniform, smooth-bordered glandular nests lined by goblet cells and admixed endocrine and Paneth cells. Occasional tubular glands were present, as were transitional type glands with both goblet cell and tubular features. Cytologic atypia was minimal, and mitotic activity was rare. Immunohistochemical studies showed positive staining of GCC tumor cells with chromogranin, cytokeratin, neuron-specific enolase, serotonin (focal), and Leu-7 (focal). The GCC component was entirely contained within the mature teratoma.