We report on a 77-year-old male patient who presented with an unusual myelogenous disorder exhibiting both myeloproliferative and dysplastic features. The patient suffered from leukocytosis, eosinophilia, basophilia, transfusion dependent anemia, and rapidly progressing thrombocytopenia. Classical chromosome analysis and fluorescence in situ hybridization (FISH) revealed a reciprocal t(3;5)(q26;q22). Using yeast artificial chromosome (YAC) probes, the breakpoint on chromosome 3 was localized to the butyrylcholinesterase (BCHE) gene (3q26.1-q26.2). This gene has recently been implicated in the regulation of myeloid cells. Whether the BCHE gene was also involved in the deregulation of myelopoiesis, causing the unusual clinical picture in this case, remains unknown.