ABSTRACT OBJECTIVE: To describe aspects of laboratory serological and molecular diagnosis of hepatitis C virus (HCV) infection in patients undergoing treatment at a dialysis clinic in Belem, Para State, Brazil, from 1990 to 1993. MATERIALS AND METHODS: Retrospective study for reassessment of serum samples from dialysed patients using serological tests for the detection of HCV (anti-HCV and Ag-Ab HCV) and HCV-RNA by molecular RT-PCR. RESULTS: A total of 115 dialysed patients with serum samples collected during the study period were included. Analysis of these samples showed a 16.5% prevalence of anti-HCV reagent, among which 4.3% showed an indicator of active viral replication (HCV-RNA reagent). Seroconversion rate was detected in 55.2% of patients in the analyzed period. The anti-HCV group, Ag-Ab HCV and HCV-RNA reagent were the most prevalent (41.7%). For non-reactive anti-HCV samples, viral replication with HCV-RNA reagent was 22.7%. Genotypes 1 and 3 were detected. Genotype 1 was prevalent in 73.0% of the samples. CONCLUSION: When laboratory screening for HCV (anti-HCV) was introduced in the dialysis clinic, it was possible to observe: high prevalence of HCV infection among patients under treatment; high rates of seroconversion; equation between serological results using second and third generation ELISA methods; presence of viral replication among nonreactive anti-HCV patients; and higher prevalence of HCV genotype 1. Keywords: Hepatitis C Virus; Serological Tests; Hemodialysis