Background: To investigate the impact of the FDA pediatric antidepressant warning in March 2004 on: 1) the treatment of new-onset depression diagnosis (NODD); 2) physician specialty practice patterns; and 3) the stock returns of the antidepressant manufacturers. Methods: Youth 2-17 years old with a NODD from 2003-2006 constituted the study population. i3 Innovus database containing administrative claims information of U.S. commercial insurance enrollees was used. National Ambulatory Medical Care Survey data (2001-2006) were used to examine antidepressant use by physician specialty during youth mental health visits. CRSP stock price data (2003-2006) was used to examine the warning impact on stock returns and volatility. Results: The warnings led to a statistically significant decrease in the likelihood of antidepressant use [Odds Ratio (OR) =0.83; CI: 0.75,0.92] and an increase in the likelihood of psychotherapy in NODD but not a significant impact on youth with MDD. The likelihood of an antidepressant prescription was significantly higher for psychiatrist visits compared to primary care (OR=3.78; CI: 2.72,5.25). The warning was associated with a non-significant impact on the magnitude of stock returns but a significant increase in the volatility of stock returns (mean change = 0.30; CI: 0.10,0.49). Conclusions: The FDA warning did not lead to a A) decrease in the likelihood of antidepressant use for youth with a diagnosis of major depression, whereas psychotherapy use increased; B) increase the likelihood of antidepressant prescribing by psychiatrists relative to primary care; C) decrease in stock returns but only a modest increase in volatility of stock returns.