PURPOSE: To describe the characteristics of episodes in which juveniles became victims of sex crimes committed by people they met through the Internet. METHODS: A national survey of a stratified random sample of 2574 law enforcement agencies conducted between October 2001 and July 2002. Telephone interviews were conducted with local, state, and federal law enforcement investigators concerning 129 sexual offenses against juvenile victims that originated with online encounters. RESULTS: Victims in these crimes were primarily 13- through 15-year-old teenage girls (75%) who met adult offenders (76% older than 25) in Internet chat rooms. Most offenders did not deceive victims about the fact that they were adults who were interested in sexual relationships. Most victims met and had sex with the adults on more than one occasion. Half of the victims were described as being in love with or feeling close bonds with the offenders. Almost all cases with male victims involved male offenders. Offenders used violence in 5% of the episodes. CONCLUSIONS: Health care professionals and educators, parents and media need to be aware of the existence, nature and real life dynamics of these online relationships among adolescents. Information about Internet safety should include frank discussion about why these relationships are inappropriate, criminal, and detrimental to the developmental needs of youth.