In the last 20 years 32 patients with severe combined immunodeficiency (SCID) were treated at our department. The clinical and immunological findings in these patients are presented. In connection with these patients, the recent WHO classification on combined immunodeficiency diseases and the pathogenesis in several forms of SCID, as far as is known, are discussed. SCID appears to represent a very heterogeneous group of disorders, which is affirmed by the findings in several of our patients. At this moment bone marrow transplantation (BMT) is the only way to cure patients with SCID. Without this treatment the prognosis of these patients is very poor. After BMT complete recovery is achieved for the majority of patients, even in the absence of a genotypically HLA identical donor. Besides the therapeutic aspects of SCID the recent developments with regard to carrier-detection and antenatal diagnosis are briefly discussed.