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Introduction: Flow cytometry is well known to detect malignant cells in peripheral blood and bone marrow of patients with hematologic malignancies. However, its role in evaluating non-hematic body fluid contamination by tumor cells is largely unexplored. Patients and Methods: Data detected by flow cytometry in non-hematic body fluid samples drawn between 2002 and 2007 from patients with hematologic neoplasms were retrospectively compared with morphological findings obtained from cytospin slides. Immunophenotyping was carried out by using disease-specific multicolor panels of quadruple monoclonal antibodies, conjugated with the fluorochromes FITC, PE, PerCP, and APC, respectively. Acquisition of information on 1x104 to 1x105 stained cells depending on the whole sample cellularity was assessed on a dual-laser FACSCalibur flow cytometer using the CellQUEST software (Becton Dickinson, San José, CA, USA). Results: Fourty-five samples (bronchoalveolar fluid, n=5; ascites, n=2; hydrocele, n=2; pleural effusion, n=8; and cerebrospinal fluid, n=28) from 32 patients were available for comparison. Diagnoses were as follows: chronic myelomonocitic leukemia (n=1), acute promyelocytic leukaemia (n=2), acute myelomonocytic leukaemia (n=1), B-chronic lymphocitic leukemia (n=4), follicular lymphoma (n=1), acute lymphoblastic leukaemia (n=6), lymphoblastic lymphoma (n=1), high grade non-Hodgkin’s lymphoma (NHL), Burkitt-like (n=3), diffuse large B-cell NHL (n=6), peripheral T-cell NHL (n=3), and NHL, unspecified (n=4). Flow cytometry detected neoplastic cells in 24 cases. Of these cases, only 17 were positive also by morphology. In 7 cases, in which tumor cells were detected by flow cytometry but not by morphology, clinical data confirmed the presence of the disease. Flow cytometry did not show neoplastic cells in 21 cases. Of these cases, only 18 were negative also by morphology. In the remaining 3, the suggestion of diffuse large B-cell NHL contamination by morphology was not confirmed by flow cytometry, demonstrating T-reactive lymphocytes that were clearly negative for disease-specific markers. Conclusions: Our data suggest that flow cytometry is a useful tool complementary to morphology for the screening of non-hematic body fluid contamination in patients with hematologic neoplasms.