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The myelodysplastic syndromes (MDS) have attracted great interest during the last decade. Unfortunately there is not much material published concerning the incidence of these conditions. We present epidemiologic data on MDS based on case registration of patients in a well‐defined population and as a comparison similar data on acute myeloid leukaemia (AML). Between the years 1978–1992 we registered 120 cases of MDS and 146 cases of AML. The median age for all the MDS cases was 74.1 years for men and 78.2 years for women. Among haematologists there is a suspicion that the incidence of MDS is rising. Our study does not support this opinion. We have divided the study period into 5‐year periods and the crude incidence has been 3.2, 4.1 and 3.5/100 000/year for each period. In the age group over 70 years MDS was more frequent than AML and in the last 5‐year period the incidence was 15.0/100 000/year for MDS compared to 10.2/100 000/year for AML. In conclusion MDS is quite common among elderly people and there is no evidence for a rising incidence during the last 15 years.

Bone marrow karyotype, survival time, and the rate of progression to leukaemia were studied in 11 1 unselected patients with primary myelodysplastic syndromes. The 49 patients (44%) with clonal chromosome aberrations had survival time (median 29 months) similar to that found in the 62 patients with normal bone marrow karyotype (24 months, p > 0.10). The presence of multiple (> 2) abnormalities (17 patients) was strongly associated with poor prognosis, with a median survival of only 7 months (p < 0.001). Prognostic information could be attributed to 2 specific abnormalities, del(5q) and -7: Presence of del(5q) as the sole anomaly was associated with long survival (36+ months), whereas monosomy 7 was a bad prognostic sign (6 months). The risk for leukaemia development correlated neither with the number of chromosome abnormalities nor with any particular anomaly. Our findings demonstrate the prognostic importance of quantifying the complexity of bone marrow chromosome changes. They also emphasize that different specific abnormalities convey widely different prognostic information in primary myelodysplastic syndromes.

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