During adolescence numerous of important social abilities are acquired within interactions with peers. Severe psychiatric disorders interfere with the acquisition of these social skills. For example, due to excessive shyness, adolescents with psychiatric disorders may not experiment positive social interactions. Social skills training (SKT) may help adolescents to remediate to these diffi culties. This exploratory study aims to assess the SKT's effect on assertivity, in a population of adolescents presenting psychiatric disorder and attending a day care unit for adolescents. The SKT, delivered in group, deals with different themes such as contact, conversation, problem solving, confl ict, fail, success, learning, effort, separation, breakdown, and project. In this context, 38 adolescents (19 suffering from anxiety / mood disorder and 19 suffering from psychotic disorder) rate their level of assertivity before and after a SKT with the Rathus assertivity scale. This scale allows to differentiate between inhibited, assertive and assertiveaggressive adolescents. Results showed a general improvement on assertivity after the SKT. More specifi cally, adolescents suffering from anxiety disorder and the 'inhibited' adolescents showed the higher benefi t from the SKT. Thus, two hours per week of SKT seems to enhance social abilities in a population with severe psychiatric disorders. More specifi - cally, adolescents with anxiety / mood disorders reported more benefi ts of the SKT on their assertivity. Nevertheless, adolescents with psychotic disorders did not report strong benefi ts from the SKT despite the improvement observed at a clinical level. This observation raises questions about the usefulness of self-reported questionnaire to measure such benefi t for adolescents with psychosis.