Non-Hodgkin's lymphomas (NHL) constitute a heterogenous group of mainly B-cell lymphoproliferative diseases with different patterns of clinical behaviour. Biological mechanisms leading to development of NHL are not clearly understood. Transforming growth factor-beta1 (TGF-beta1) influences B cell growth and development. The present study aimed to determine whether there is an association between the polymorphic features located within the TGF-beta1 gene in NHL patients and progression of the disease. Two single nucleotide polymorphisms at positions 869 T/C (Leu10Pro) and 915 G/C (Arg25Pro) in the precursor region of the TGF-beta1 gene were determined in 55 NHL patients and 50 healthy individuals by PCR-SSP technique using commercial primers. In univariate analysis the presence of TGF-beta1 high producer genotypes (T/T G/G or T/C G/G) was found to significantly associate with an increased number of extranodal sites (11/30 vs 3/25, p=0.035 for two or more extranodal sites in patients having or lacking the TGF-beta1 high producer genotype, respectively). TGF-beta1 high producer genotype together with other clinical and biological factors (patient sex and age, stage and aggressiveness of the disease, presence of B symptoms, serum LDH level) were subjected to multivariate logistic regression analyses for the number of extranodal sites. Multivariate analysis confirmed the role of TGF-beta1 high producer genotype as a risk factor of NHL manifestation in two or more extranodal sites (OR=7.217, p=0.043) in addition to histological aggressiveness of the disease (OR=4.302, p=0.057). TGF-beta1 gene polymorphisms were found to associate with the course of the disease in NHL patients. TGF-beta1 high producer genotype appeared as an independent risk factor of extranodal manifestation of the disease.