Background and aims: Despite the availability of several drug consumption rooms (DCR) in different European countries few epidemiological studies have evaluated their benefits. A network of DCR for people who inject drugs (PWID) has existed in Catalonia since 2000. We aimed to study the impact of frequently attending DCR on injecting in public, infectious risk (disposal of used syringes in safe places, sharing needles and/or injecting equipment), accessing drug dependence services and non-fatal overdoses. Methods: In 2014-2015, we performed the cross-sectional study REDAN in Catalonia's network of harm reduction centres (needle exchange programs, outreach programs, and DCR). A sample of current PWID were recruited. Self-reported data about risky and other behaviours and about access to care were collected through anonymous face-to-face structured interviews. Oral fluid samples were also collected to test for HIV and HCV antibodies. Multiple logistic regressions were used to assess the impact of frequently attending DCR on the different outcomes. Results: Among the 730 PWID recruited, 510 reported attending DCR in the previous 6 months, of whom 21.2% were `frequent' attenders. After multiple adjustment, frequent attenders had a 61% lower risk of injecting in public (AOR [95%CI]:0.39[0.18-0.85]) and sharing needles or other injecting equipment (0.39[0.18-0.85]) than `medium' and `low' attenders. They were six times more likely to place used syringes in a safe place (6.08[3.62-10.23]) and were twice as likely to access drug dependence services (2.56[1.44-4.55]). No significant effect was found for non-fatal overdoses, perhaps because of survival bias. Conclusion: The multiple benefits found strongly advocate for the maintenance of current DCR and the promotion of new DCR, in conjunction with other harm reduction strategies, in European countries where they are not yet available.