This longitudinal study explored associations between psychosomatic symptoms in adolescence and mental health symptoms in early adulthood. The baseline data were collected in 1996 from 14-year-old pupils (n = 235; 116 girls, 119 boys) at schools using a structured questionnaire that included a 14-item scale of psychosomatic symptoms. The follow-up data were collected in 2006 from the same persons at the age of 24 using the Symptom Checklist-90. Follow-up questionnaires were returned by 149 (63.4%) young adults (88 women and 61 men). Young adults who had many psychosomatic symptoms in adolescence suffered more often than the others from somatization and anxiety symptoms in early adulthood. In addition, women had more symptoms of depression and paranoid ideation, and men had more interpersonal sensitivity and psychotic symptoms. Psychosomatic symptoms in adolescence might be important signals of mental health and this should be taken seriously in school health and in general primary care.