Abstract Systemic release of tumor necrosis factor (TNF) and lymphotoxin-α (LTα) has been found to contribute to the severity of non-Hodgkin's lymphoma (NHL). We investigated whether genetic polymorphisms in the TNF locus, previously shown to influence TNF and LTα genes expression, might contribute to these cytokines production and to the clinical course of NHL. Genomic DNA from 273 lymphoma patients was typed for TNF (−308) polymorphism using an allele-specific polymerase chain reaction (PCR) and for LTα (+252) polymorphism with a PCR-based restriction fragment length polymorphism. The presence of the TNF allele involved in increased TNF gene transcription was associated with higher plasma levels of this cytokine at the time of lymphoma diagnosis (χ2 test, P = .013). An extended haplotype analysis showed that the presence of at least two TNF or LTα high-producer alleles constituted a risk factor for first-line treatment failure (χ2 test, P = .021), shorter progression-free survival (log-rank test, P = .0007), and overall survival (log-rank test, P = .012). In the subgroup of 126 patients with diffuse large-cell lymphoma, the presence of two or more TNF/LTα high producing alleles contributed significantly to a higher rate of relapse and progression (log-rank test, P = .045 and P = .027). In multivariate Cox regression models including the variables of the International Prognostic Index, the TNF/LTα haplotype status was found to be an independent risk factor for progression-free survival (relative risk 2.33, 95% confidence interval [1.17 to 4.64], P = .0053) and overall survival (relative risk 1.92, 95% confidence interval [0.63 to 5.80],P = .081) of large-cell lymphoma patients. These results indicate that genetic polymorphism leading to increased TNF production influences the outcome of NHL and suggest a pathophysiological role for the genetic control of the immune response in lymphoid malignancies.