Understanding the trajectories of youths within Child and Adolescents Mental Health Service (CAMHS) is of primary importance. Our objective is to assess the usefulness of the Health of the Nation Outcome Scales for Children and Adolescents (HoNOSCA) to predict inpatient (IP) stay for youths followed by assertive community treatment (ACT) teams. 82 youths followed exclusively by ACT and 42 who needed IP were assessed with the HoNOSCA at admission to the program. The HoNOSCA allowed the computing of three scores: a total score, an externalizing symptoms (Ext) score and an emotional problems (Emo) score. Logistic regressions revealed that the three HoNOSCA scores at admission of ACT predicted later need for hospitalization. Using ROC curve analyses, we set up cut off scores with appropriate sensitivity and specificity for the HoNOSCA Total and Ext to optimally predict the need for hospitalization. This study revealed that the HoNOSCA may be a useful tool to predict the need for later IP during ACT. Such knowledge is important to set up the best therapeutic strategies.