A newly-updated document by the Vatican concerning the training of priests insists spiritual directors should "dissuade" any such individual from pursuing ordination.
It says: "The Church, while profoundly respecting the persons in question, cannot admit to the seminary or to holy orders those who practice homosexuality, present deep-seated homosexual tendencies or support the so-called 'gay culture'."
The document, entitled 'The Gift of Priestly Vocation' continues: "Such persons, in fact, find themselves in a situation that gravely hinders them from relating correctly to men and women.
"One must in no way overlook the negative consequences that can derive from the ordination of persons with deep-seated homosexual tendencies."
The report, which is called Ratio Fundamentalis Institutionis Sacerdotalis in Latin, was first issued by the Vatican's Congregation for the Clergy in 1970 and updated in 1985.
Cardinal Beniamino Stella from the Congregation for the Clergy said the guidance "needed to be revamped, renewed, and restored to the centre", to take into account "historical, socio-cultural, and ecclesiastical contexts."
The document goes on to say the case would be "different" for an individual experiencing homosexual tendencies "that were only the expression of a transitory problem - for example, that of an adolescence not yet superseded".
It adds: "Nevertheless, such tendancies must be clearly overcome at least three years before ordination to the diaconate."
The Gift of Priestly Vocation also sets out a new "propaedeutic" or induction period to the Seminary of between one and two years, and it emphasises the need for leaders to guard against "admitting potential sex abusers to the priesthood."