Background: Injecting drug users are at increased risk for harmful effects compared to non-injecting drug users. Some studies have focused on differences in characteristics between these two groups (e. g., housing, overall health). However, no study has investigated the specific Dutch situation which in the last years has seen a decrease in homelessness among problematic hard-drug users and an increasing focus on physical health in low-threshold addiction care. The purpose of this study was to determine differences in sociodemographic, drug use and health characteristics between never-injecting (NIDUs), former-injecting (FIDUs) and current-injecting drug users (IDUs) and describe injecting practices. Methods: A total of 202 problematic hard-drug users (NIDU = 64; FIDU = 76; IDU = 62) were recruited from 22 low-threshold care facilities, including drug consumption rooms, methadone maintenance treatment, heroin-assisted therapy, day shelter and/or night shelter, supported housing and day activity centres. Data were collected on-site through structured face-to-face interviews. Results: Results indicate that IDUs represented a separate group of problematic hard-drug users, with distinct sociodemographic and drug use characteristics. Overall, IDUs appeared to be the group with least favourable characteristics (unstable housing/homelessness, illegal activities, polydrug use) and NIDUs appeared to have the most favourable characteristics (stable housing, help with debts, less polydrug use). The FIDU group lies somewhere in between. The three groups did not differ significantly in terms of health. Regarding injecting practices, results showed that majority of IDUs had injected drugs for over 10 years and IDUs injected heroin, cocaine, amphetamine and/or methadone in the past 6 months. Sharing syringes was not common. A quarter reported public injecting. Conclusions: Unstable housing and homelessness are related to (former) injecting drug use, and stable housing is related to never-injecting drug use. Our study suggests ...