According to the Catechism of the Catholic Church (1511, 1514, 1515):
The Church believes and confesses that among the seven sacraments there is one especially intended to strengthen those who are being tried by illness, the Anointing of the Sick.
This sacred anointing of the sick was instituted by Christ our Lord as a true and proper sacrament of the New Testament. It is alluded to indeed by Mark, but is recommended to the faithful and promulgated by James the apostle and brother of the Lord.
The Anointing of the Sick “is not a sacrament for those only who are at the point of death. Hence, as soon as anyone of the faithful begins to be in danger of death from sickness or old age, the fitting time for him to receive this sacrament has certainly already arrived.”
If a sick person who received this anointing recovers his health, he can in the case of another grave illness receive this sacrament again. If during the same illness the person’s condition becomes more serious, the sacrament may be repeated. It is fitting to receive the Anointing of the Sick just prior to a serious operation. The same holds for the elderly whose frailty becomes more pronounced.
This Sacrament is conferred by a priest. The pastor always brings the anointing oils to all hospital and sick calls. Anyone else experiencing a serious sickness can request the sacrament, as well as those preparing for a major surgery.