Objectives: To compare substance use, gambling behaviors and personality traits between two different groups of individuals with a gambling disorder (young and adult patients); to explore the contribution of sex, age and personality traits on substance use; and to evaluate the capacity of age and personality traits to predict substance use. Methods: The participants were 428 gambling disorder (GD) patients, divided into two groups based on age [55 young participants (age≤25 years) and 373 middle- to old-aged participants (age>25 years)]. All were consecutively admitted to a Psychiatry Department and diagnosed according to the DSM-IV criteria. In addition, the Diagnostic Questionnaire for Pathological Gambling according to DSM-IV criteria, the South Oaks Gambling Screen (SOGS), the Temperament and Character Inventory-Revised (TCI-R), and other clinical measures were used to examine gambling behaviors, substance use and personality. Results: When the two age groups were compared, statistically significant differences were observed in several sociodemographic variables. Furthermore, the younger GD patients presented higher rates of drug use (p=.010). Regarding the personality traits, differences were found only in the Novelty Seeking (NS) scale, where the younger patients presented elevated scores (p=.006). Higher scores (p=.022) in NS and lower ones (p=.028) in Self-Transcendence (ST) were the personality traits significantly associated with tobacco consumption (p=.003). However, only age was associated with other substance use (p=.003).