In "Light of the World: The Pope, the Church and the Signs of the Times," the pontiff tells German writer Peter Seewald homosexuality is a great trial with which a person may be faced, the Italian news agency ANSA reported.
However, the pope said being gay "remains something that is against the nature that God originally willed."
In the 18-chapter book released Tuesday, Seewald asked the pope 90 questions, a number dealing with homosexuality.
Benedict stressed priests cannot be gay, adding that great care must be taken to ensure priestly celibacy "is not identified with a tendency towards homosexuality.
In an excerpt of the book reported earlier the pope said condoms might be justified in certain rare cases to prevent the spread of disease.