Recommendations for universal screening of patients with cancer for hepatitis B virus (HBV), hepatitis C virus (HCV), and human immunodeficiency virus (HIV) are inconsistent. A recent multisite screening study (S1204) from the SWOG Cancer Research Network found that a substantial number of patients with newly diagnosed cancer had previously unknown viral infections. The objective of this study was to determine the cost-efficiency of universal screening of patients with newly diagnosed cancer. We estimated the cost-efficiency of universal screening of new cancer cases for HBV, HCV, or HIV, expressed as cost per virus detected, from the health care payer perspective. The prevalence of each virus among this cohort was derived from S1204. Direct medical expenditures included costs associated with laboratory screening tests. Costs per case detected were estimated for each screening strategy. Secondary analysis examined the cost-efficiency of screening patients whose viral status at cancer diagnosis was unknown. Among the possible options for universal screening, screening for HBV alone ($581), HCV alone ($782), HBV and HCV ($631) and HBV, HCV, and HIV ($841) were most efficient in terms of cost per case detected. When screening was restricted to patients with unknown viral status, screening for HBV alone ($684), HBV and HCV ($872), HBV and HIV ($1,157), and all three viruses ($1,291) were most efficient in terms of cost per newly detected case. Efficient viral testing strategies represent a relatively modest addition to the overall cost of managing a patient with cancer. Screening for HBV, HCV, and HIV infections may be reasonable from both a budget and clinical standpoint. Significance: Screening patients with cancer for HBV, HCV, and HIV is inconsistent in clinical practice despite national recommendations and known risks of complications from viral infection. Our study shows that while costs of viral screening strategies vary by choice of tests, they present a modest addition to the cost of managing a patient with cancer.