Doubt remains about the need for residential substance user treatment for young cannabis users. Using a series of validated clinical tools, this study compared 1,221 primarily cannabis-, psychostimulant-, alcohol-, or opioid-dependent young people admitted to an urban/rural Australian residential treatment program between 2001 and 2007. Multinomial logistic regression revealed that the cannabis user group had poorer mental health than the opioid group, poorer social functioning than the alcohol drinking group, and comparably poor functioning otherwise but remained in treatment longer than the psychostimulant and opioid user groups. Residential treatment for primarily cannabis-dependent young people with complex and multiple needs can be supported.