http://codes.lp.findlaw.com/uscode/18/I/117/2423
(a) Transportation With Intent To Engage in Criminal Sexual
Activity. - A person who knowingly transports an individual who has
not attained the age of 18 years in interstate or foreign commerce,
or in any commonwealth, territory or possession of the United
States, with intent that the individual engage in prostitution, or
in any sexual activity for which any person can be charged with a
criminal offense, shall be fined under this title and imprisoned
not less than 5 years and not more than 30 years.
(b) Travel With Intent To Engage in Illicit Sexual Conduct. - A
person who travels in interstate commerce or travels into the
United States, or a United States citizen or an alien admitted for
permanent residence in the United States who travels in foreign
commerce, for the purpose of engaging in any illicit sexual conduct
with another person shall be fined under this title or imprisoned
not more than 30 years, or both.
(c) Engaging in Illicit Sexual Conduct in Foreign Places. - Any
United States citizen or alien admitted for permanent residence who
travels in foreign commerce, and engages in any illicit sexual
conduct with another person shall be fined under this title or
imprisoned not more than 30 years, or both.
(d) Ancillary Offenses. - Whoever, for the purpose of commercial
advantage or private financial gain, arranges, induces, procures,
or facilitates the travel of a person knowing that such a person is
traveling in interstate commerce or foreign commerce for the
purpose of engaging in illicit sexual conduct shall be fined under
this title, imprisoned not more than 30 years, or both.
(e) Attempt and Conspiracy. - Whoever attempts or conspires to
violate subsection (a), (b), (c), or (d) shall be punishable in the
same manner as a completed violation of that subsection.
(f) Definition. - As used in this section, the term "illicit
sexual conduct" means (1) a sexual act (as defined in section 2246)
with a person under 18 years of age that would be in violation of
chapter 109A if the sexual act occurred in the special maritime and
territorial jurisdiction of the United States; or (2) any
commercial sex act (as defined in section 1591) with a person under
18 years of age.
(g) Defense. - In a prosecution under this section based on
illicit sexual conduct as defined in subsection (f)(2), it is a
defense, which the defendant must establish by a preponderance of
the evidence, that the defendant reasonably believed that the
person with whom the defendant engaged in the commercial sex act
had attained the age of 18 years.