Background: Gambling disorder, previously known as pathological gambling (PG), is the only behavioural addiction included in the revised Diagnostic and Statistical Manual of Mental Disorders (5th ed.; DSM-5, American Psychiatric Association, 2013) chapter on Substance-Related and Addictive Disorders. Not only is PG often comorbid with substance use disorder, but the two disorders are also more common in individuals with impulsive personality including individuals with antisocial personality disorder (ASPD). This research investigated the association between PG and ASPD and to identify risk factors for the traits in a Thai methamphetamine-dependent sample. Methods: Demographic and diagnostic data (based on DSM-IV; American Psychiatric Association, 1994) were obtained from 728 methamphetamine-dependent individuals using the Semi-Structured Assessment for Drug Dependence and Alcoholism (SSADDA), as part of an ongoing study of the genetics of methamphetamine-induced psychosis in a Thai substance dependence treatment cohort. Associations between PG and ASPD were analyzed using the chi-square test. Risk factors for PG and ASPD were identified by logistic regression analysis. Results: The comorbidity of PG and ASPD with methamphetamine dependence was high (33.4% and 23.8% respectively). Individuals with ASPD were more likely to have PG than those without (49% vs. 29%; chi(2)(1) = 25, p < 0.001). The only demographic variable associated with PG and ASPD was male sex (PG: OR = 1.4, p = 0.05; ASPD: OR = 2.5, p < 0.001). Youth (age < 20 years) predicted a diagnosis of ASPD (OR = 3.1, p < 0.001). In addition, a host of substance dependence variables were associated with both PG and ASPD, including severe methamphetamine dependence (PG: OR = 2.2, p = 0.001; ASPD: OR = 1.8, p = 0.04), nicotine dependence (PG: OR = 1.8, p = 0.002; ASPD: OR = 1.6, p = 0.04), and alcohol dependence (PG: OR = 1.5, p = 0.02; ASPD: OR = 1.7, p = 0.007). Cannabis use was associated with PG (OR = 1.6, p < 0.001), opiate use (OR = 2.1, p = 0.002) and occurrence of methamphetamine-induced paranoia (OR = 1.7, p = 0.009). Conclusions: Risk factors common to PG and ASPD were gender, substance dependence and severity of substance dependence. ASPD but not PG was associated with neuropsychiatric disorders. In methamphetamine-dependent individuals age was a predictor for a diagnosis of ASPD suggesting pathophysiological differences in the basis of substance dependence in different age groups.