The hepatitis C virus (HCV) shows a wide genetic variability. The different variants of HCV have been classified into 9 types and different subtypes. Some genotypes have a characteristic geographic distribution and seem to be associated with precise ways of contagion. Serum samples from 107 spanish patients with chronic hepatitis C were studied, which were distributed as follows: 88 parenteral drug addicts (PDA) and a control group of 19 subjects made up by 4 transfused, 5 probably sexually infected and 10 with unknown contagion source (sporadic cases). HCV typing was made by means of the PCR method and later hybridization analysis with complementary probes of different types and subtypes of HCV exposed on a smooth surface (Inno-LiPA). A total to 105 (98.4%) patients had their viruses genotypes. There was more than one genotype in the same subject (co-infection) in 43.8% of cases and co-infection 1a + 1b was the most common (82.7%). While not reaching a statistic significance, co-infections were more frequent in PDA (47.1%) than in the remaining patients (27.8%). In the infected patients with only one genotype, the most common genotype was 1a, both in PDA (22.9%) and in subjects with transfusional HCV, sexual or sporadic (38.9%). In decreasing frequency came genotypes 1b (13.3%) and 3a (11.4%). Other genotypes were very uncommon (2a and 4) or were absent (2b and 5) as unique infections. In conclusion, genotypes non-1b of HCV, mainly 1a and to a lesser extent 3a, are the most common in a spanish population made up mainly by young persons with risk antecedents for HIV infection, particularly PDA. Furthermore, co-infection with HCV genotypes is frequent in this population.