Overall, 9 percent of teenagers, or 2.2 million, were depressed, with older teens more at risk than their younger peers, said the Substance Abuse and Mental Health Services Administration, or SAMHSA.
About 12 percent of youths aged 16 or 17 faced severe depression in 2004, compared with about 5 percent of those 12 or 13 years old. Among those aged 14 or 15, 9 percent experienced a major episode.
"These new data serve as a wake-up call to parents. Mental health is a critical part of the overall health and well-being of their children," said SAMHSA Administrator Charles Curie.
Major depression was considered a period of at least two weeks that included a loss of interest, depressed mood and at least four other symptoms such as a change in sleeping, eating or concentration.
Doctors said the findings showed more needed to be done to help teenagers early on, but were not surprising.
"The real tragedy, as the report notes, is that there are still so many young people who aren't receiving the appropriate and effective treatment they need and deserve," Dr David Fassler, a psychiatry professor at the University of Vermont, said in an e-mail to Reuters.
SERIOUS ILLNESS Dr Bennett Leventhal, a professor of child and adolescent psychology at the University of Illinois in Chicago, said the number of depressed teens had hovered at about 10 percent for 15 to 20 years.
"Despite the fact that it's common and has a huge impact on children and their lives, we're not addressing this very serious illness," he told Reuters.
Adding to treatment difficulties, said Leventhal, were a limited number of specialised caregivers, insurance issues and difficulty among parents and teachers in noticing the symptoms.
Treatment for depression among teenagers became a controversial issue when a US Food and Drug Administration scientist concluded in early 2004 that anti-depressants posed a suicide risk in youth. Another university-sponsored study showed a similar link.
The FDA has since required drug manufacturers to disclose the possible risk on labels for anti-depressants. Some experts, including doctors, worried the warning would lead to fewer youths receiving treatment.
Thursday's findings, part of the agency's annual National Survey on Drug Use and Health, also showed very depressed adolescents aged 12 to 17 were twice as likely to engage in substance abuse than those who were not depressed.
About 28 percent of depressed teens used alcohol, while nearly 23 percent smoked cigarettes and about 21 percent used drugs.
Among those who did not report a major episode, about 17 percent drank alcohol, about 11 percent smoked, and about 10 percent used drugs.
The report surveyed 70,000 people in the United States aged 12 and older.