Both the key mechanism of action for marijuana (the endocannabinoid system) and the symptoms associated with marijuana withdrawal suggest an important link to anxiety. Despite this link, there is a dearth of research on the characteristics of heavy marijuana users with clinical-level anxiety compared to those with heavy marijuana use alone. Over 10,000 participants (friends or affiliates of the National Organization for the Reform of Marijuana Laws) provided data via online survey. After careful, conservative screening, anxiety, other psychopathology, other drug use, and marijuana-related problems were examined in 2567 heavy marijuana users. Subsequently, 275 heavy users with clinical-level anxiety were compared to demographically-equivalent non-anxious heavy users on psychopathology, drug use, and cannabis-related problems. Among several psychological variables (including anxiety, depression, schizotypy, and impulsivity), anxiety was most strongly predictive of amount of marijuana used and marijuana-related problems. Group comparison (n=550 total) revealed that clinically anxious heavy users exhibited more use, more non-anxiety psychopathological symptoms, and a greater number and severity of marijuana-related problems than their non-anxious peers. The findings reveal that anxiety shows an important relation to marijuana use and related problems among regular, heavy users. Further examinations of common and unique factors predisposing individuals for anxiety and marijuana abuse appear warranted.