Although cannabis is a relatively benign drug, at least compared with some other illegal drugs, most Australian States and Territories prohibit its use, possession, or sale. In 1999 there were 7,820 appearances in New South Wales local courts in which at least one of the charges was for cannabis use or possession. This bulletin reports the results of a representative survey of 19- to 29-year-olds to identify the reasons people give for never using cannabis, determine the reasons people give for not using cannabis over the last 12 months, and assess whether those who currently use the drug would consider using it more often if it were legalized. Findings suggest that the illegal status of cannabis does act to limit its use; however, fear of arrest, fear of imprisonment, the cost of cannabis, or its availability do not appear to exert much effect on the prevalence of cannabis use, although they may exert some restraining effect on cannabis consumption among frequent cannabis users. Health considerations and anticipated or actual dislike of the drug are more important factors in preventing or stopping its use. Its legal prohibition was the third most frequently cited reason for nonuse or desistance from use. These findings do not support claims that the legalization of cannabis use would not result in any increase in the number of people using the drug. 4 tables, 3 figures, 15 references, and appended questionnaire