The study explores the qualifications and competency needs of professionals working at Swedish Maria clinics, specialized in treating youth with co-occurring substance use and mental health problems. A web-based survey was conducted among 87 professionals working at the clinics to assess their qualifications, competence in managing co-occurring problems and perceived needs for further training. Most professionals had high educational qualifications, with backgrounds in social work, nursing and psychology. Although health care and social services professionals had generally similar competencies, there were some notable differences in their professionalism and competency needs. Healthcare professionals were more likely to report competence in managing severe psychiatric conditions. In contrast, social services professionals more often reported using a broader range of treatment methods. Both groups identified a need for further education in managing severe psychiatric conditions, such as trauma, psychosis and eating disorders. Social services professionals more frequently emphasized the need for family-oriented approaches, while healthcare professionals more often identified a need for more in-depth knowledge related to substance use. While professionals at the clinics generally possess strong qualifications, there are differences in their confidence and expertise relating to managing complex mental health conditions. Tailored training initiatives that address specific needs based on professionals’ educational backgrounds and organizational affiliations could enhance inter-professional collaboration and improve treatment outcomes for youth with co-occurring substance use and mental health problems.