Background: Hepatitis C virus (HCV) infection is a neglected disease in patients with cancer. Therefore, this study examined the impact of HCV infections in these patients. Methods: The records of HCV-infected patients with cancer seen at The University of Texas MD Anderson Cancer Center (2008–2011) were reviewed. The outcomes of those who underwent HCV treatment were analyzed. Results: Of 1291 patients who had positive test results for an antibody to HCV (anti-HCV), 744 (58%) were tested for HCV-RNA; 642 (86%) of which had chronic HCV infections. Most had solid tumors (72%) and genotype-1 (G-1) infections (66%). HCV therapy was administered in 348 patients (98 of them after cancer diagnosis). Sustained virologic response (SVR) occurred in 27 (35%) of the 78 patients treated for whom outcome data were available. Compared with patients who experienced an SVR, more patients who did not were black (29% vs 4%; P=.007), had G-1 infections (72% vs 6%; P<.0001), and had higher baseline aspartate aminotransferase (78 vs 47 IU/L; P=.006) and alanine aminotransferase levels (71.1 vs 43.3 IU/L; P=.009). Overall, progression to cirrhosis (hazard ratio [HR], 0.38; P=.03) and portal hypertension (HR, 0.19; P=.009) was less common in those treated, irrespective of the treatment outcome (SVR or non-SVR). Hepatocellular carcinoma (HCC) developed as a second primary malignancy in 7% of patients with non-HCC cancer. Conclusions: This is the largest series to analyze HCV infections in patients with cancer. HCV therapy is feasible and prevents liver disease progression in this forgotten population. A treatment algorithm is provided.