T-lymphoblastic lymphoma is a high-grade malignant lymphoma with frequent occurrence in young males, mediastinal involvement, and systemic dissemination. Indolent T-lymphoblastic proliferations have rarely been recognized. In the present case, we report on an indolent T-lymphoblastic proliferation involving the oropharynx in a patient with myasthenia gravis with multiple local recurrences over an 11-year period without evidence of systemic dissemination. The T-lymphoblasts were consistently positive for terminal deoxynucleotidyl transferase (TdT), CD1, CD3, CD4, and CD8, corresponding to an intermediate thymocyte stage of differentiation. No cytokeratin-positive thymic epithelial cells were identified, ruling out an ectopic thymus or thymoma. T-receptor gene rearrangement studies by Southern blot revealed no monoclonal CT-beta rearrangement. Indolent T-lymphoblastic proliferations of undetermined clonality may rarely occur; predilection for involvement of oropharynx and possible association with myasthenia gravis are suggested.