Objective: To analyze sociodemographic factors, injection behavior, and the prevalence of hepatitis C and human immunodeficiency virus (HIV) among injection drug users (IDUs) in five cities of Colombia.Methods: We carried out a cross-sectional study of 1,123 people, using respondent-driven sampling (RDS). Prevalence of hepatitis C and HIV was estimated. The association between sociodemographic factors, injection behavior, and prevalence of hepatitis C and HIV syringe exchange was established, and raw and adjusted prevalence ratios were calculated.Results: Forty point three per cent of users share needles. Among IDUs, the HIV prevalence was 5.5%, and hepatitis C prevalence was 31.6%. Being male reduces the likelihood of sharing syringes. On the other hand, a secondary level of education, exchanging another part of the equipment and the increased consumption of crack are associated with syringe exchange.Conclusions: The existence of injector networks in cities of Colombia, and a lot of sharing of non-sterile and unclean injection equipment were recognized.