The aim of this study was to analyze the clinical features and laboratory findings of adult Epstein-Barr virus associated T/NK cell lymphoproliferative disease (EBV+T/NK-LPD) and to investigate the early diagnosis and prognosis of EBV+T/NK-LPD. The clinical data of 19 adult patients with EBV+T/NK-LPD were retrospectively analyzed. The results indicated that there were 11 males and 8 females. The median age was 32 years (range: 20-70 years). The average duration from onset of symptoms to diagnosis was 3.5 months. The median survival time was 2.5 months. Unkown fever, hepatosplenomegaly, liver dysfunction and interstitial pneumonia were the main clinical features. High levels of β2-MG, LDH, TNF, IL-6 and significantly increased EBV-DNA level (median level > 10(6) copies/ml) were occurred in all the patients. Cytopenia was seen in 18 cases. Morphologically, atypical large granular lymphocytes and hemophagocytosis were common in bone marrow smears. Deletion of CD5 or CD7 were frequently observed in T/NK lymphocytes in bone marrow cells by flow cytometry. Bone marrow biopsy showed atypical lymphocyte interstitial infiltrated in 10 cases, while a few large cells infiltrated in 6 cases. Immunohistochemistry showed the expression of CD3(+)CD56(+) were seen in 2 cases, CD3(+)CD8(+) in 11 cases and CD3(+)CD4(+) in 3 cases. TIA-1 and EBER were positive in all biopsy specimens. Three cases underwent biopsy of lymph nodes showed reactive proliferations of lymphocytes. All the patients died of multiorgan failure. It is concluded that the fever, hepatosplenomegaly are the most common clinical features in adult EBV+T/NK-LPD, the bone marrow infiltration of EBV-infected T/NK lymphocytes and significantly increased EBV-DNA level can be observed in all cases, the clinical outcome of this disease is poor, these clinical and experimental features can be served as a reliable marker for the timely diagnosis of adult EBV+T/NK-LPD.