Background: There is concern about the prevalence of prescribing antidepressant medications to youth without appropriate diagnoses or who have subthreshold (mild) depression. Methods: Electronic records data from 3 large healthcare systems identified youth aged ≤21 years starting a new episode of antidepressant treatment between January 1, 2009, and December 31, 2013. For those with a diagnosis of depression, Patient Health Questionnaire (PHQ9) scores at the time of treatment initiation were used to examine the distribution of symptom severity and patients' demographic and clinical characteristics. Results: Of the 15,460 episodes of treatment, a depression diagnosis was recorded in 95% of the cases. PHQ9 scores were available for 4,329 youth with a diagnosis of depression. Younger age, sex, previous treatment, co-occurring anxiety, treatment setting, concurrent psychotherapy, and site were significant predictors of completing a PHQ9. Among youth with a baseline score, 87% reported moderate or severe symptoms (PHQ9 score ≥ 10) and 13% reported mild or minimal symptoms (PHQ9 < 10). The proportion reporting PHQ9 < 10 when starting treatment decreased with age, ranging from 19% in those aged 13–14 years and 12% in those aged 18–21 years. Patients treated by psychiatrists were 1.54 times (95% Confidence Interval [CI], 1.21–1.97) more likely to have PHQ9 scores < 10 compared with primary care physicians. Patients with prior treatment history (odds ratio = 1.76; 95% CI, 1.45–2.13) and concurrent psychotherapy (odds ratio = 1.24; 95% CI, 1.02–1.52) were more likely to have PHQ9 < 10. Conclusions: In these health systems, prescribing of antidepressant medication to adolescents for minimal or mild depression is much less common than previous reported.