This case describes the clinical course of a cannabis-dependent individual entering a 12-week abstinence-based research program. The case illustrates the effects of chronic, heavy cannabis use on executive functions at three time points: 1) 24 hours of abstinence; 2) 4 weeks of abstinence; and 3) 12 weeks of abstinence. It is followed by discussions by two clinical psychologists and a psychiatrist. The findings described here have important clinical implications, as executive functions have a vital role in treatment participation and in sustaining recovery. It should be of particular interest to clinicians who work with people with cannabis use disorders.