Thirteen adults between the ages of 20 and 41 years, all of whom smoked cannabis products intensively (three to ten times per week) for a period of 16 months to six years, were seen during the period of 1969 through 1971. They all demonstrated symptoms that simultaneously began with cannabis use and disappeared within 3 to 24 months after cessation of drug use. In addition, a correlation of symptoms was observed in relation to the duration and frequency of smoking. When coupled with the stereotyped nature of the symptoms regardless of psychological predisposition, a consideration of biochemical and structural changes in the central nervous system (possibly cerebral cortex) as a result of intensive cannabis use seemed to be in order. It would appear that the present medical and public approach to education regarding the danger of marihuana use should undergo some reassessment.