The estimates presented were derived from three components of the second National Incidence Studies of Missing, Abducted, Runaway, and Thrownaway Children (NISMART-2): the National Household Survey of Adult Caretakers, the National Household Survey of Youth, and the Juvenile Facilities Study. The NISMART-2 studies covered the years 1997 to 1999. Because the majority of cases were from the studies conducted in 1999, the annual period used in this bulletin was 1999. In 1999 an estimated 1,682,900 youth had a runaway/thrownaway episode. Of these youth, 37 percent were missing from their caretakers, and 21 percent were reported to authorities for purposes of locating them. Of the total runaway/thrownaway youth, an estimated 1,190,900 (71 percent) could have been endangered during their runaway/thrownaway episode by virtue of factors such as substance dependency, use of hard drugs, sexual or physical abuse, presence in a place where criminal activity was occurring, or extremely young age (13 years old or younger). Two-thirds of the youth with runaway/thrownaway episodes during 1999 were between the ages of 15 and 17. There is suggestive evidence that the runaway problem may have been smaller in 1999 than in 1988. 5 tables