In this article, we present the case of a 57-year-old man with cervical and mediastinal tumor mass, normal blood count as well as virusological status. Cervical tumor tissue biopsy revealed cells positive for CD34, CD13, LCA, CD33, and CD163 but negative for T-cell and B-cell markers, NK-cell markers, plasmacytic markers and anaplastic large cell lymphoma markers. These features were consistent with myeloid sarcoma of the neck with involvement of the mediastinum. We discussed differential diagnosis and therapy of isolated myeloid sarcoma and suggest that clinical presentation, cell morphology, complete immunophenotype, and specific genotypic lesions in some cases, must be evaluated.