OBJECTIVE:To report nationally representative findings on the prevalence, correlates, psychiatric comorbidity and treatment of DSM-IV Cannabis Use and Cannabis Use Disorders in Australia. METHOD:The 2007 National Survey of Mental Health and Wellbeing was a nationally representative household survey of 8841 Australians (16-85 years) that assessed symptoms of the most prevalent DSM-IV mental disorders. RESULTS:Prevalence of lifetime and 12-month cannabis use was 18% and 6%; prevalence of lifetime and 12-month cannabis use disorder was 6% and 1%. The conditional prevalence (proportion of ever users who met criteria for a disorder) of lifetime and 12-month cannabis use disorder was 32.2% and 14.3%. Current cannabis use disorders were more common in males (OR 2.0) and younger users (OR 4.6). Strong associations were observed between current cannabis use disorders and alcohol use disorders (OR 3.6) and current affective disorders (OR 3.0). Only 36.2% of those with current cannabis use disorders sought any treatment. CONCLUSIONS:The prevalence of cannabis use disorders in the Australian population is comparable with that in the USA. Current cannabis use disorders are highly concentrated in young Australians who have high levels of comorbidity. The low rates of treatment seeking warrant attention in treatment and prevention strategies.