The present study compares dual-diagnosis patients with other groups of psychiatric patients to determine the differential characteristics in suicide risk and other clinical variables between them. During 2008 in Madrid, 837 outpatients were evaluated in addiction and mental health services. Three comparison groups were created according to current diagnosis: (i) dual patients, (ii) patients with substance use disorders but no other mental disorders, and (iii) patients with mental disorders but no substance use disorders. A multinomial logistic regression model was built to explore the risk associated with dual diagnosis. Criteria for dual diagnosis were met at the time of the study by 440 patients (52.6%). Dual patients showed several demographic and clinical differences and a higher risk for suicide than the other two comparison groups. Further research is needed to define suicide preventive strategies for dual patients.