The frequencies, kinds, pathogens, and risk factors of infections in the myelodysplastic syndromes (MDS) were analysed in 430 cases. The overall tendency was for one infectious episode per 1023.5 patient days. The frequency of infectious episodes was highest just after diagnosis of MDS when more than 4 episodes per 1000 patient days occurred. Thereafter, the rate declined rapidly to about 0.3 episodes per 1000 patient days within 4 years. The most frequent infection was that of the respiratory tract followed by sepsis and fever of unknown origin (FUO). Among the types of infection resulting in death, sepsis and FUO comprised the highest proportion (40%) followed by respiratory tract infections (39%). The most frequent pathogen observed was Staphylococcus bacteria. The significant multivariate risk factors for fatal infections were subtype, hemoglobin, dependence on red blood cell transfusion, age, and sex. A staging system was created using these five simple variables at diagnosis.