purpose: To determine the incidence, characteristics, and outcome of infection in patients with myelodysplastic syndromes (MDS) and risk factors that may lead to infection. patients and methods: We reviewed infections that occurred in 86 consecutive patients with MDS who received care from 1968 to 1986 at a university-affiliated Veterans Affairs Medical Center. Time lines charting the course of each patient with MDS were created and included infections, MDS subgroup at the time of presentation and at the time of each infection, peripheral neutrophil counts, and therapies for MDS. results: Infections occurred at a rate of nearly one per patient year of observation. Infection rates were associated with MDS subgroup as follows: refractory anemia with or without ringed sideroblasts (RA ± RS) less than refractory anemia with excess blasts (RAEB) less than RAEB in transformation (RAEB-T). The group of RA ± RS patients who had erythroid abnormalities but minimal or no dyspoiesis of other cell lines had the lowest rate of infections. Infection rates were higher in patients with less than or equal to 1,000 neutrophils/μL blood than in patients with greater than 1,000 neutrophils/μL blood for each classifiable MDS subgroup. Neutrophil concentration and MDS subgroup were independent risk factors for infection in patients with MDS. Bacterial pneumonias and skin abscesses were the most common infections. Infection was the most common cause of death during MDS, accounting for 64% of deaths, and was more common than transformation to acute leukemia as a cause of death. conclusion: Infection is a common, lifethreatening problem in patients with MDS. Neutropenia and MDS subgroup are each risk factors for infection. Clinicians should aggressively evaluate patients with fever and MDS for infection, especially pneumonia and skin infections.