Rosai-Dorfman disease (RDD) is a rare histiocytic condition of unknown etiology. Patients with RDD classically present with massive painless cervical lymphadenopathy. However, extra-nodal disease occurs in approximately 40% of cases, with the skin being among the most commonly involved sites. Patients with isolated extra-nodal involvement may present without adenopathy. Reports of RDD occurring in patients with Hodgkin's lymphoma, and B-cell lymphoma have been published, but there has only been one previous report of RDD in a patient with a T-cell lymphoma. This case report documents a unique combination of RDD and mycosis fungoides (MF), a cutaneous T cell lymphoma. This report also highlights diagnostic challenges in RDD due to the rarity of the condition and its variable presentation.