This study applied a solution-focused single session therapy (SST) approach to all clients presenting to an urban child and adolescent mental health clinic over 14 months. The effectiveness of a single 2-hour assessment and treatment session in treating mental health problems was investigated using parent, teacher and clinician outcome measures. Teachers reported low levels of psychopathology at intake with no significant change 1 month after treatment. However, using parent and clinician measures, clinical levels of psychopathology were found at intake, with significant improvement 1 month after a single session of treatment. The effect sizes for these improvements measured medium to large, demonstrating observable improvement of clinical significance from the 1 session of SST treatment. Respondents reported 95% satisfaction with service. The study adds weight to the argument that a solution-focused SST approach can be effective for the treatment of children and adolescents with mental health problems. It recommends SST as the initial choice of treatment for these clients.