This report describes characteristics of lymphoma-associated hemophagocytic syndrome (LAHS) in 142 patients throughout Japan who were enrolled in a questionnaire survey. The 68 patients with B-cell LAHS (B-LAHS) were older on average than the 64 who had T-cell or natural killer-cell LAHS (T/NK-LAHS) (median ages at diagnosis: 63.5 versus 49 years). However, the clinical signs of cytopenia, coagulopathy, and liver dysfunction were generally less severe in the former group than in the latter. Furthermore, the prognosis was better for the B-LAHS group than the T/NK-LAHS group (median survival: 242 days versus 69 days). The Epstein-Barr virus genome was detected by EBERs in situ hybridization in 3 of 24 B-LAHS patients examined, and in 19 of 23 T/NK-LAHS patients. Based on observed clinical manifestations, T/NK-LAHS was subdivided into 2 types: LAHS that developed in patients with nasal or nasal-type NK/T-cell lymphoma during their clinical course; and LAHS as the initial presentation in T/NK-cell lymphoma patients with hepatosplenomegaly and without lymphadenopathy. In B-LAHS, hemophagocytic syndrome was the major initial symptom, and patients had hepatosplenomegaly without lymphadenopathy. Also, 10 of 20 B-LAHS patients demonstrated intravascular lymphomatosis. Based on the findings of this survey, we proposed a set of new diagnostic criteria for LAHS.