The present study analysed the clinicopathological features of nine myelodysplastic syndrome (MDS) patients in which del(20q) was the sole cytogenetic abnormality and a control group of 17 adult patients with idiopathic thrombocytopenic purpura (ITP). Seven of nine del(20q) patients were thrombocytopenic and six of nine were mildly anaemic at presentation. There was no significant morphological dysplasia identified in the del(20q) group as compared with the ITP group. These results indicate that MDS with del(20q) commonly presents with thrombocytopenia and has minimal morphological dysplasia. Cytogenetic analysis on adult patients undergoing bone marrow sampling for thrombocytopenia may help avoid misdiagnosis of MDS with del(20q) as ITP.