The study aimed to examine demographic and psychosocial features of clients presenting to a new community addiction service in Dublin by retrospective collection of data from the National Drug Treatment Reporting System and from case records on site. The setting was Ballymun Addictions Service, where adequate records were available for three-quarters of all cases seen to date. Findings included a mean age of injecting commencement of 18 years, a 7-year period of injecting before treatment entry, 80% hepatitis C infection rate, 39% prevalence of heroin-addicted siblings, 73% within-family substance misuse, 80% male previous conviction rate and universal early school leaving. Psychosocial problems included domestic violence, sexual assault, homelessness, self-harm, teenage sex work and homicide history. It is concluded that the caseload of the community-based addiction service includes many complex problems and that prognosis for most clients must be guarded. Community-based treatment services need to address the endemic and collective nature of addiction processes in the poverty context.