Motivation is considered a pivotal factor in treatment, but a better understanding of this topic is needed. Drieschner et al. (Clin Psychol Rev 23:1115–1137, 2004) proposed to distinguish treatment motivation and treatment engagement. This study aimed to discover whether it is possible to identify classes of adolescents with severe psychiatric problems having comparable profiles of treatment engagement. To this end, professionals filled out the Treatment Engagement Rating Scale 5 times for 49 adolescents (mean age 18.3 years; SD = 1.6) during the first year of case management treatment. Using a longitudinal latent class analysis, the number of profiles of treatment engagement was investigated and described. Results identified three profiles: high (19 clients, 39 %), medium (20 clients, 41 %) and low (10 clients, 20 %). Adolescents with a high engagement profile were at first equally, and later on more engaged in treatment than clients with a medium engagement profile. Adolescents with a low engagement profile made the least effort to engage, except after 30 weeks. Adolescents with a low engagement profile were often substance-dependent males with the lowest scores on the Global Assessment of Functioning Scale after a year. Only adolescents with a high engagement profile improved on global functioning. In conclusion, it is possible to identify different treatment engagement profiles by asking one question about level of global treatment engagement. Frequent assessment of engagement of the individual client as well as including a behavioural component into assessment and treatment may help to improve case management treatment for adolescents with medium and low engagement profiles.