We describe a 47-year-old male admitted with fever and extreme neutrophil granulocytosis (up to 80 x 10(9)/L). All microbiology tests and test for autoimmune disease were negative. CT scan showed pulmonary infiltrates bilaterally, mediastinal lymphadenopathy and splenomegaly. Conventional pathological examination of bone marrow and lymph node biopsies did not demonstrate malignant cells and inflammatory disease was suspected. The patient died of multiorgan failure 23 days after admission. Autopsy showed neutrophil infiltration of several organs. Immunohistochemistry and cytogenetics postmortem led to a diagnosis of anaplastic large cell lymphoma (ALCL) of T-cell lineage. Involvement of peripheral blood with leukemoid reaction is a rare manifestation of ALCL. This case emphasizes the importance of immunophenotyping in unexplained extreme granulocytosis.