Some retrospective studies suggest an association between infection with GB-virus C (GBV-C) and non-Hodgkin lymphoma (NHL). We evaluated this association prospectively in a nested case-control study within the U.S. Prostate, Lung, Colorectal and Ovarian Cancer Screening Trial (PLCO). Cases (N=658) and controls (N=1,316) were individually-matched by age, sex, race/ethnicity, timing of study entry and sample selection. Pre-diagnostic PLCO serum samples were tested for GBV-C RNA (as a measure of active infection) and E2 antibody (active or resolved infection). Logistic regression was used to estimate odds ratios (ORs) for the association between GBV-C and NHL overall and NHL subtypes. Twelve cases (1.8%) and 7 controls (0.5%) were GBV-C RNA positive. GBV-C RNA positivity was associated with NHL overall (OR=3.43, 95% CI=1.35-8.71) and, based on small numbers, diffuse large B-cell lymphoma (OR=5.31, 95% CI=1.54-18.36). The association with NHL persisted when the interval between testing and selection was greater than 4 years (OR=6.00, 95% CI= 1.21-29.73). In contrast, E2 antibody-positivity was not associated with NHL risk (OR=1.08, 95% CI=0.74-1.58). Our study demonstrates that GBV-C infection precedes development of NHL. GBV-C infection may play an etiologic role in a small proportion of NHL cases, perhaps by causing chronic immune stimulation or impaired immunosurveillance.