As of February, 1998 about 130 thousand AIDS cases were reported in Brazil; 21% of them among injecting drug users (IDUs). The present paper reviews the main findings of the HIV epidemiology and other blood-borne pathogens infection among IDUs, in Brazil and abroad, to foster the ongoing research and preventive initiatives carried out in Brazil. Data have shown that, far from the stereotype of a male population living in the main metropolitan areas, IDU population is rather heterogeneous. This population is under continuous turnover, with relevant changes in its very composition, habits and drug consume patterns. An accurate estimation of the size of IDU population in different settings and places is a puzzling task, although recent methodologies, e.g. capture-recapture methods, seem to be a reliable strategy. The use of combined data from different sources is also very useful in the process of population size estimation. Comprehensive researches carried out in different settings, using data from distinct and complementary aggregation levels, under regular follow-up, are essential to monitor patterns and trends of the drug users population and drug consume patterns, especially the injection of illicit drugs. These data are essential to the implementation and permanent evaluation of preventive strategies, as well as tools for the optimal allocation of scarce resources. Due to the double risks to which IDUs are exposed – parenteral and sexual – different infections are frequent in this population, taking place in an early moment of their drug use “career”. Successful interventions must be precocious and comprehensive, providing counseling, testing for different pathogens, and access to condoms and sterile injection equipment. Another core interventions set involves the prevention of the transition from non-injecting to injecting routes, and efforts to offer low-threshold and available anonymous treatment at no cost for either their clinical problems and harms secondary to drug abuse.