Ensuring that the voices of youths are heard is key in creating services that align with the needs and goals of youths. Concept mapping, a participatory mixed-methods approach, was used to engage youths, families, and service providers in an assessment of service gaps facing youth in an underserviced neighborhood in Toronto, Canada. We describe 6 phases of concept mapping: preparation, brainstorming, sorting and rating, analysis, interpretation, and utilization. Results demonstrate that youths and service providers vary in their conceptualizations of youth service needs and priorities. Implications for service planning and for youth engagement in research are discussed.