After controlling for history of depression and gender, seven of the nine DSM-III-R symptoms of depression predicted MDD incidence when tested in separate models. The presence of each symptom increased the likelihood of MDD onset over a 1-year interval. Consistent with the study hypothesis, mood disturbance predicted the incidence of MDD in the subsequent year. No other symptom contributed unique variance to the prediction of MDD, which suggests that co-occurrence of symptoms, more than the strength of a single individual symptom, is what constitutes the greatest risk. The presence of sad mood contributes additional unique variance to the prediction of MDD and supports the centrality of depressed mood in MDD. Data for this analysis came from the Oregon Adolescent Depression Project, a prospective epidemiological study of psychological disorder among adolescents, ages 14 to 18 years old, from the general community. A total of 1,709 adolescents completed the initial diagnostic assessments between 1987 and 1989 (T1); and approximately 1 year later (T2), 1,507 adolescents returned for readministration of assessments (88-percent response). 3 tables and 32 references