Background: The onychodystrophies associated with Sézary syndrome (SzS) have rarely been described in the literature. We performed a retrospective analysis of SzS patients at a single institution and compared our data with previous publications. Objectives: The objectives of this study were to identify and describe the most frequent nail alterations in patients with SzS. Methods: A retrospective analysis was performed with some prospective observations at the University of Pittsburgh from 1989 to 2017. Results: We identified 54 patients with SzS out of 535 patients with cutaneous T-cell lymphoma. Nineteen patients with SzS had photos of their nail. All those patients exhibited some type of onychodystrophy. The most common types were paronychia (63.2%; 12/19), leukonychia (42.1%; 8/19), onycholysis (42.1%; 8/19), trachyonychia (31.6%; 6/19), and subungual hyperkeratosis (26.3; 5/19). Cluster analysis of our data in comparison with published data on the psoriatic nails indicated that while leukonychia, onycholysis, subungual hyperkeratosis, and nail discoloration were frequently observed in psoriasis, onychauxis, anonychia, distal notching, and onychoschizia occurred more commonly in patients with SzS. Conclusions: The most common nail manifestations in SzS patients included paronychia, leukonychia, and onycholysis. The nail manifestations in SzS patients appeared to be heterogeneous, while onychauxis, anonychia, distal notching, and onychoschizia seem to be specific to SzS in comparison with psoriasis.