Sezary syndrome (SS) is a rare subtype of cutaneous T-cell lymphoma (CTCL) marked by erythroderma, circulating neoplastic T cells, and poor prognosis. Its belongs to the group of non-Hodgkin's lymphomas (NHL) resulting from malignant proliferation of skin-homing T cells. We report through a series of 6 cases, the experience of the hematology laboratory in the diagnosis of the syndrome of Sezary. Methods: This is a retrospective study of 6 cases of Sezary syndrome collected in the dermatology and hematology Departments Mohammed VI University Hospital of Marrakech. Results: six patients were identified with the clinicopathological criteria of SS. At the time of diagnosis, 5 patients had erythroderma and generalized lymphadenopathy in both superficial and deep stations. The white blood cell count was elevated (>10,000 WBC/mm3) in 3 patients. The blood smear showed the presence of small to medium-sized cells with a high nucleo-cytoplasmic ratio and cerebriform nuclei typical of Sezary cells and suggests the diagnosis of SS in all cases. Conclusions: The diagnosis of SS remains a challenge in many situations; the pathophysiology and definition of SS have evolved significantly over the past decades.