Abnormalities of chromosome 5 and 7 are frequently found in primary MDS. Cases with familial monosomy 7 are well recognized, but there are no reports of familial MDS with deletion of 5q. We describe two sisters, aged 38 and 36 years, both of whom had MDS and interstitial deletion of 5q. The occurrence of this chromosomal abnormality reinforces the concept of tumour suppressor gene hypothesis in some cases with familial MDS.