Less than 2% of all lymphoproliferative diseases are indolent or small T-cell disorders, and include T-cell chronic lymphocytic leukemia (CLL)/prolymphocytic leukemia (PLL), large granular lymphocyte (LGL) leukemia, and mycosis fungoides (MF). T-PLL has an aggressive clinical course characterized by high lymphocyte counts, marked hepatosplenomegaly, anemia, thrombocytopenia, and median survival times less than 1 year. The majority of cases are associated with abnormalities of chromosome 14. T-CLL probably represents a small cell variant of T-PLL with a similar aggressive course and similar cytogenetics. T-LGL leukemia is a clonal disorder of CD3+, cytotoxic T lymphocytes. Common clinical features include neutropenia, anemia, splenomegaly, and recurrent bacterial infections. The prognosis is dictated by the severity of the neutropenia, with 10-year actuarial survival rates greater than 80%, and most deaths related to sepsis. A small subset of LGL leukemias have a natural killer (NK) phenotype, are refractory to treatment, and result in multiorgan failure and death in a few months. Mycosis fungoides (MF), the most common of the small T-cell disorders, is a cutaneous T-cell lymphoma with a chronic course, often extending over decades, with most patients eventually succumbing to infection. The small T-lymphocyte disorders represent a rare, diverse group of diseases, which generally have an indolent course, but are not curable.