Extramedullary myeloblastic tumors, so-called myelosarcomas (granulocytic sarcomas, chloromas) have been reported only sporadically in the pertinent literature which reflects their rather infrequent occurrence. These lesions may accompany the initial manifestation or signal relapse of acute myeloid leukemia (AML) or coincide with blastic transformation of a chronic myeloproliferative disorder. However, even more rarely, primary myelosarcomas may precede AML by months or years or may be associated with myelodysplastic syndromes (MDS) that never progress to manifest leukemia. In a retrospective evaluation a clinicopathological study on these latter two variants of isolated extramedullary manifestations of AML was performed to elucidate certain aspects of site involvement and histopathology by application of enzyme and immunohistochemistry. For this reason, we selected 6 patients presenting with a myelosarcoma in combination with MDS and 12 patients revealing only uncharacteristic reactive changes of the bone marrow. Of these patients 8 developed AML following an observation time of up to 2 years. Focal leukemic infiltrates were most often localized in the skin ( n=4), oral mucosa ( n=4), lymph nodes ( n=3), gastrointestinal tract ( n=3) or pleura and retroperitoneum ( n=3 each). Myelosarcomas were usually regarded by the clinicians as putative malignant lymphomas unless further evaluation, especially involving chloroacetate esterase reactions as well as immunostaining with a panel of antibodies reactive with lysozyme, myeloperoxidase, CD68, CD43, CD56, CD117 and CD34 proved their true nature. Although at that time bone marrow findings were inconclusive, a straightforward diagnosis was reached by considering the possibility of a (primary) myelosarcoma in these patients.