Background: Impairments in decision making are a consistent finding in substance use disorder (SUD) populations. However, decision‐making deficits are not specific for SUDs and are also reported in the context of other psychiatric disorders such as antisocial and borderline personality disorders (PDs). Given the frequent comorbidity between SUD and cluster B PD, it might be questioned whether the decision‐making impairments typically reported in SUD populations reflect the addictive disorder, the cluster B PD, or a combination of the 2.Methods: In the current study, we compare the decision‐making performance of non–substance‐abusing controls (n=53) on the Iowa Gambling Task (IGT) with the decision‐making performance of 3 abstinent alcohol‐dependent samples, i.e., alcoholic patients without any PD (n=38), alcoholic patients with a cluster A or C PD (n=19), and alcoholic patients with a cluster B PD (n=23).Results: Overall, all 3 alcohol‐dependent subsamples performed inferior compared with controls. Between alcoholic subsamples, the alcoholic patients with a cluster A or C PD had the highest IGT score, followed by the alcoholic patients without a PD, while the cluster B alcoholic patients were the most impaired.Conclusion: These findings suggest that impairments in decision making underlie both alcohol dependence and cluster B PD, and alcoholic patients with a comorbid cluster B PD are particularly impaired in their decision making. These deficits may underlie the severe problems that characterize cluster B alcoholic patients specifically in inappropriate behaviors (e.g., poly substance abuse, legal, and professional dysfunction).