Background The potential risk for transmission of hepatitis C virus (HCV) by peritoneal dialysis (PD) has been studied previously, with conflicting results. Methods To assess whether HCV crosses the peritoneal membrane, the following determinations were performed in 16 patients (7 males, 9 females; mean age 41.8 years; mean time on PD 14 ± 15 months) undergoing PD: serum anti-HCV using second-generation enzyme-linked immunosorbent assay (ELISA), serum and PD fluid HCV RNA by nested polymerase chain reaction, HCV genotyping by restriction fragment length polymorphism, and serum HCV load by branched DNA assay. Results Anti-HCV was positive in 10 patients. Serum HCV RNA was positive in 7 anti-HCV-positive patients and negative in all anti-HCV-negative patients. Fluid HCV RNA was detected in 5 (71.4%) patients testing positive for serum HCV RNA and in none testing negative for serum HCV RNA. Serum HCV genotype was 1a in 3 patients and 1b in 4; PD fluid HCV genotype was 1a in 1 patient and 1b in 4. Genotypes in serum and fluid were concordant when both were positive. Serum viral load ranged from nondetectable by the quantitative method to 5.1 MEq genome/mL in patients with fluid infection, and 1.05 MEq and 29 MEq genome/mL in the remaining 2 patients without detectable HCV in PD fluid. Conclusions HCV crosses the peritoneal membrane and may be detected in the dialysate of PD patients with proven viremia. Although our study population was small for firm conclusions to be drawn, this passage does not seem to depend upon the serum viral load. Our data support the notion that PD fluid needs careful handling and local disinfection to prevent possible spreading of viruses, in the institutional and the domestic environments.