Grey-platelet syndrome is a rare familial platelet impairment characterised by lack of alpha granules and giant vacuolated platelets. A Mexican family with grey-platelet syndrome associated to Marfan disease is presented. The family was comprised of 22 members, of whom 3 (the propositus and two of his nephews) could be studied. Two of them, with haemorrhagic symptoms since childhood, had moderate prolongation of the Ivy bleeding time which improved after DDAVP administration, plus moderate thrombocytopenia, giant platelets and abnormal platelet aggregation induced by adrenalin, ADP and collagen. Platelet factor 4 was normal. Electron microscope examination of platelets showed lack of alpha granules and increased dense bodies. The rarity of the casual association of two low-frequency genetic diseases, namely Marfan disease and the grey-platelet syndrome, is commented, along with the response attained with DDAVP in the two affected individuals.