BACKGROUND: Acute tumor lysis syndrome(TLS) has been defined as the metabolic abnormalities that occur after rapid tumor breakdown. In this study, we have evaluated the types or degrees of metabolic abnormalities and clinical characteristics in patients with non-Hodgkin's lymphoma(NHL) who developed TLS. METHODS: Patients were considered to have 'laboratory TLS(LTLS)' if any two of the following metabolic abnormalities occurred spontaneously or within 4 days of treatment: hyperphosphatemia, hyperkalemia, hyperuricemia, azotemia, and hypocalcemia. 'Clinical TLS(CTLS)' was defined as LTLS plus one of the following: a serum potassium level greater than 6.0mEq/L, a creatinine level greater than 2.5mg/dL, a calcium level less than 6.0mg/dL, the development of a life-threatening arrhythmia, or sudden death. RESULTS: Of 111 cases with NHL, TLS occurred in 16(14.4%), LTLS in 11(9.9%), and CTLS in 5(4.5%). There was a significant difference of gender, histologic type, clinical stage, performance status, extranodal involvement, serum lactate dehydrogenase(LDH), LDH index, beta2-microglobulin, uric acid, and blood urea nitrogen(BUN) level in the TLS versus control group. In multiple regression analysis, TLS occurred more frequently in patients with pre-treatment azotemia, aggressive histologic type, and elevated serum LDH level(p< 0.05, respectively). Pre-treatment and post-treatment TLS occurred in 8 cases(50%) respectively. The common metabolic abnormalities included hyperphosphatemia(87.5%), azotemia(81.3%), and hypocalcemia(75%). Of 11 cases with conservative care, 8 cases recovered within several days, but 3 cases died with multi-organ failure from disease progression. All 5 cases after hemodialysis for TLS recovered without any significant complications. CONCLUSION: The current study suggests that all patients with high-grade lymphomas and pre-treatment azotemia or a high serum LDH level be carefully monitored for at least 4 days after chemotherapy.