Although dual disorders (DD), addiction, and other mental disorders (MDs) are common in patients using mental health and addiction treatment services, they are not routinely screened for and diagnosed by most health experts. The aim of this article was to present the most relevant findings from the Madrid study on DD in a clinical sample from the Community of Madrid mental health and substance misuse service care networks. The sample consisted of 837 outpatients from Madrid: 208 patients from mental health services and 629 from substance misuse services. We used the Mini International Neuropsychiatric Interview (MINI) to evaluate Axis I MDs and the Personality Disorder Questionnaire (PDQ4+) to evaluate personality disorders (PDs). DD cases were those in which there was a current diagnosis of an addictive disorder (excluding nicotine addiction) and another MD including PDs. The DD prevalence rate was 61.8%. There were differences in the prevalence figures for the 2 types of service: 36.1% in mental health services and 70.3% in substance misuse services. Among dual diagnosis patients there were fewer male individuals, a higher rate of unemployment, and higher figures for alcohol and cannabis dependence than among addicts only (n=194). There were differences in several sociodemographic characteristics, and dual diagnosis patients were associated with diagnoses of bipolar disorders, agoraphobia, generalized anxiety disorder, and posttraumatic stress disorder. They also presented a greater suicide risk and had more PDs than patients with MD diagnoses only, excluding substance use disorders (n=126). There is a high prevalence of DDs among those seeking treatment, more so in substance misuse services than in mental health services, and they have different characteristics that suggest greater severity. These findings could be of help in planning care service policies for these patients.