This chapter delves into mycosis fungoides (MF) and Sézary syndrome (SS), the most prevalent forms of primary cutaneous T-cell lymphomas. Classic MF (Alibert-Bazin type) progresses from early patch and plaque stages to tumor formation and systemic involvement. Clinical variants, such as folliculotropic MF, granulomatous MF, and γδMF may have worse prognosis. Sézary syndrome is a leukemia-lymphoma characterized by erythroderma, lymphadenopathy, and circulating malignant cells. A significant portion of the chapter addresses histological and immunohistochemical features critical for diagnosis, highlighting the challenges of differentiation from benign conditions. Treatment strategies are tailored to disease stages, ranging from skin-directed therapies like phototherapy to systemic interventions for advanced cases. The chapter also incorporates disease-related comorbidities and long-term management to improve survival and quality of life.