B-cell chronic lymphocytic leukaemia and the similar diseases are seen predominantly in patients above the age 50 years, i.e. at the age when the patients also have other co-morbidities. The knowledge of these diseases on molecular level has improved significantly over the last decade. Molecular and biological prognostic factors are available in routine everyday practice. Assessment of these factors enables prediction of prognosis and, in some cases, also the response to therapy. The aim of the present review is to provide the medical community with the main information on this disease as patients with B-cell chronic lymphocytic leukaemia and similar disease states are of older age and very often suffer from a range of co-morbidities. Consequently, care for these patients involves physicians from various specialities. The aim of the following text is to present a clear overview of the basic information about this group of diseases that might be useful to all physicians who provide care to patients with B-cell chronic lymphocytic leukaemia and similar conditions. Since monoclonal immunoglobulin is sometimes identified in patients with these diseases, it is important to consider these conditions in the differential diagnosis of the states with the presence of monoclonal immunoglobulin.