Background. Although a great deal of evidence is available on the patterns and determinants of unmet health care needs among adolescents with mental health problems, little is known about the factors that influence the need for care. The aim of this study is to assess the occurrence of need for care for mental problems in adolescents and the determinants of this need. Methods. Data were obtained from three assessment waves of TRAILS (TRacking Adolescents' Individual Lives Survey) (N = 1406). Need for care was assessed at age 16/17 (parent report). Determinants concerned previous health care utilization, emotional and behavioral problems (child behavior checklist and youth self-report) and child and family characteristics. Results. Of the 1406 parents, 409 parents (29%) reported that their child needed help for mental problems. Of these adolescents, only 29% received specialized mental health treatment. The determinants of need for mental health care at age 16/17 were family break-up and parental internalizing problems (age 10/11), parent-reported internalizing and externalizing (age 10/11 and 13/14) and receiving specialized help (age 13/14). Conclusion. A substantial proportion of all adolescents need care for their mental problems, according to their parent. There is also a large group of adolescents with mental health problems according to their parents, but for whom no parental reported need for care is expressed. The findings stress the importance of early interventions focusing on raising parental and child awareness of mental health problems.