A rare and primitive myelodysplastic syndrome 5q(-) is characterised first, by the persistence of the cytogenetic anomaly 5q(-), and second, by its feminine predominance. Among 13 cases of myelodysplastic syndromes, the subject of a substantial and systematic cytogenetic medullar study (1996-1998), this paper is a case study of 2 syndromes 5q(-) diagnosed in two male patients, respectively, aged 41 and 68. The following diagnosis was made on the basis of an aregenerative macrocytic anaemia, a high platelet count, and a megakaryocytic hyperplasia, along with dysmegakaryocytopoiesis. The diagnosis of the 5q(-) syndrome was verified by cytogenetic analysis showing in one of the patients a deletion 5q(-)(q13, q33) and 5q(-)(q14, q34) with trisomy in the second one. Treatment was only limited to a blood transfusion. Subsequently one of the patients developed an advanced case of leukaemia. This paper suggests that a systematic medullar cytogenetic study must be conducted in the case of any refractory anaemia in order to identify the syndrome 5q(-) in individual cases.