We report on 37 adults aged 50 years or less with de novo myelodysplastic syndrome (MDS) (excluding cases secondary to chemo or radiotherapy), who represented 6.7% of our total cases of adult MDS. Median age was 42 (range 18-50). At diagnosis, there were 9 RA, 6 RAEB, 13 RAEB-T, 9 CMML but no RARS. Five patients had a familial history of MDS, and 3 a history of occupational exposure to potential carcinogens. Twenty-one patients received intensive chemotherapy (at diagnosis or during the evolution) but only 8 (38%) achieved complete remission (CR), and median CR duration was 10 months. Five patients were allografted (3 of them as first line therapy): 2 remained disease free after 12 and 10 months, and 3 died of transplant related complications. Median actuarial survival of the 37 patients was 21 months. Significantly shorter survival was seen in patients who had circulating blasts, Bournemouth score greater than 1 or 2, abnormal karyotype (especially monosomy 7) and RAEB or CMML. When compared with our MDS aged more than 50, our MDS aged 50 or less were characterized by more familial cases, more cases of RAEB-T and less cases of RAEB and RARS, more frequent abnormal karyotype and monosomy 7, more frequent progression to AML, identical overall survival but longer survival in RAEB-T and shorter survival in CMML. MDS in younger adults seem relatively often familiar or associated to occupational exposure. They have a poor prognosis with conventional therapeutic approaches and therefore require allografting, whenever possible.