Gambling disorder (GD) often co-occurs with other behavioural addictions and mental health concerns. The Adcom program in Madrid, Spain, was designed so that people can self-refer if they believe they have a behavioural addiction. In this study, the researchers examined the clinical, sociodemographic, and psychological characteristics of people who self-referred to Adcom for GD. In addition, predictors of GD associated with online versus offline gambling were assessed. It was found that the majority of people with GD experienced other mental health issues. Many also had another behavioural addiction or substance use disorder. Being born in Spain and excessive internet use were unique predictors of online GD relative to offline GD. These results could inform researchers and clinicians.