We studied the incidence of myelodysplastic syndrome (MDS) in a population served by one district general hospital over a 10-year period (1981-90). Cases were sought through investigation of individuals presenting with suggestive peripheral blood findings. 279 new cases were diagnosed in a population rising from 203,000 to 226,000 over the study period. The observed incidence rate did not change over the study period. The crude incidence rate was 12.6/100,000/year. Age-specific incidence rates per 100,000 per year were 0.5 for age < 50, 5.3 for age 50-59, 15 for age 60-69, 49 for age 70-79, and 89 for age 80+. A cohort study of one large general practice revealed several previously unknown and asymptomatic cases, indicating that the observed figures for the population overall may still underestimate the real incidence. We conclude that MDS is more common than reported in previous studies and that incidence continues to rise into very old age. Difficulties in case ascertainment hamper reliable estimates of true incidence.