This article examines the stability of symptoms, syndromes, and diagnoses of specific anxiety and depressive disorders, as well as diagnostic shifts from one syndrome to another over time. Using retrospective and longitudinal prospective data from the baseline and first follow-up investigation (19.7 months later) of the Early Developmental Stages of Psychopathology Study (EDSP), we focus on establishing stability measures for early stages of mental disorders in a community sample of adolescents aged 14 to 17 years at baseline. The results are as follows: (1) Although only about 30% developed a full-blown DSM-IV disorder, psychopathological syndromes are widespread in adolescents: 15% of the population aged 14 to 17 at baseline were not affected by at least some clinically relevant symptoms of mental disorders either throughout their previous life or throughout the follow-up period. (2) The likelihood of staying free of symptoms and threshold disorders during follow-up was highest among subjects who were completely well at baseline. The probability of a positive outcome decreased as a function of severity of baseline diagnostic status. (3) There was a considerable degree of fluctuation not only in the diagnostic status and severity of specific disorders, but also in terms of complete remissions and shifts from one syndrome and disorder to another. (4) Anxiety disorders, overall, slightly differ with regard to the persistence and stability of the diagnostic status from depressive disorders. (5) However, there were remarkable differences between specific types of anxiety and depressive disorders. Consistent with other longitudinal epidemiological studies in the general population, this study finds that the syndromes and diagnoses of mental disorders have a strong tendency to wax and wane over time in this age group.