The aim of the study was to determine excess mortality associated with cannabis use disorders. Individuals entering treatment for cannabis use disorders were followed by use of Danish registers and standardized mortality ratios (SMRs) estimated. Predictors of different causes of death were determined. A total of 6445 individuals were included and 142 deaths recorded during 26,584 person-years of follow-up. Mortality was predicted by age, comorbid use of opioids, and lifetime injection drug use. For different causes of death the SMRs were: accidents: 8.2 (95% CI 6.3-10.5), suicide: 5.3 (95% CI 3.3-7.9), homicide/violence: 3.8 (95% CI 1.5-7.9), and natural causes: 2.8 (95% CI 2.0-3.7). Following exclusion of those with secondary use of opioids, cocaine, amphetamine, or injection drug use, SMRs for all causes of death remained significantly elevated except for homicide/violence. The study underlines the need to address mortality risk associated with cannabis use disorders.