We describe four patients with a mature T-cell disorder. These four specific entities belong to a group formerly called "T-cell chronic lymphocytic leukaemia" (T-CLL). Nowadays we understand that these chronic T-cell lymphoproliferative disorders consist of four different entities. They stand out as well-described and separate disorders on the basis of their clinical, immunophenotypic and cytogenetic properties. Unfortunately, the majority of patients have a bad response to chemotherapy. The purine analogs may offer a better prognosis for some patients.