A 66-year-old female patient complained of loss of body weight and fatigue. The clinical examination revealed a thrombocytosis with a maximum count of 3.200 . 10(9) platelets and a leukocytosis with maximally 25 . 10(9) white cells in the peripheral blood. The bone marrow showed a large increase of megakaryocytes. Under the diagnosis of megakaryocytic myelosis a chemotherapy with 186 mg busulfan was performed. In the course of this treatment the clinical picture of a sepsis occurred which could not be controlled by antibiotics. The patient died four months after her admission to the clinic. The essential findings in autopsy were a caseous tuberculosis of the lymph nodes with haematogenic generalization which appeared as a septic tuberculosa gravissima ("typhobacillosis" Landouzy). The bone marrow was atrophic. Spleen liver and lymph nodes were without evidence for a myeloproliferative disorder. Thus, the initial diagnosis had to be changed to a megakaryocytic pseudomyelosis with massive thrombocytosis as a reaction to the tuberculous infection. The differential diagnosis of megakaryocytic myelosis, other disorders of the myeloproliferative syndrome, and the reactive thrombocytosis are discussed.