Previous research has consistently documented high rates of tobacco smoking and substance use disorders among people with serious mental illness. However, limited studies have been conducted outside traditional clinical settings. In an attempt to address this shortfall and to better understand the needs of people accessing its services, a national community managed mental health service (Neami) examined the prevalence and impact of substance use among 489 consumers from across Australia. Results indicated extremely high rates of tobacco use, with 64.8% of participants identified as daily smokers. Approximately 86% of participants met abuse or dependence criteria for their caffeine use. In addition, 27.6% met criteria for an alcohol use disorder, whilst 28% met criteria for a cannabis use disorder. Overall rates of other illicit substance use were low. This study reinforces the need for routine alcohol and drug screening and assessment across all mental health settings, as well as appropriate support strategies that address high level smoking and caffeine intake.