Pope Francis says he is “worried” about the “serious issue” of homosexuality in the clergy.
He said gay people should not join the Catholic clergy and that homosexuality had become “fashionable”.
Talking about potential priests, the pope said: “The issue of homosexuality is a very serious issue that must be adequately discerned from the beginning with the candidates.
“In our societies it even seems that homosexuality is fashionable and that mentality, in some way, also influences the life of the church.”
His comments were published in the book The Strength of a Vocation, which was released at the weekend.
The pontiff said: “This is something I am concerned about, because perhaps at one time it did not receive much attention.”
He said candidates for the priesthood, as well as women seeking to become nuns, must be “humanly and emotionally mature”.
He added: “For this reason, the church urges that persons with this rooted tendency not be accepted into ministry or consecrated life.
“It’s better for them to leave the ministry or the consecrated life rather than to live a double life.”
The Catholic Church believes homosexual acts are sinful.
In 2013, the pope reaffirmed this stance, but said homosexual orientation was not sinful.
“If a person is gay and seeks God and has good will, who am I to judge?” he said.