Halacha requires one to stand when his father or mother enters the room. Of course, this obligation assumes that the person had been sitting before the parent entered; if he had already been standing, then he simply remains standing. However, Rav Yosef Shalom Elyashiv (contemporary) rules that if a person is standing and knows that his parent is coming into the room, he should preferably sit so he could then stand when the parent enters and thereby fulfill the Misva of honoring parents.
An interesting question arises in the case of a parent who, Heaven forbid, suffers from Alzheimer’s Disease or a similar disorder that causes memory loss, and does not recognize the child. Does the obligation to stand in a parent’s presence apply even in this case, or is the child exempt from standing, given that the parent would not even notice that the child stands? One might argue that since standing would have no effect on the parent, who, unfortunately, does not even recognize the child and would not feel honored, the child is not required to stand in such a case.
Rav Elyashiv, however, rules that a child must stand in honor of the parent even in such a case. The Gemara comments that honoring parents is akin to honoring the Shechina (the Divine Presence). Even if the parent will not take note of the expression of honor, the Almighty most certainly will. The obligation to show honor to parents therefore applies even if the parent will not feel the honor displayed by the child.
The Halacha to stand when a parent enters applies even during transit, such as if a person is on a train, airplane or bus when the parent boards. Even in these cases, the child must rise when the parent enters.
According to Sephardic practice, one must stand each time a parent enters, regardless of how many times this occurs throughout the day. Of course, this may cause considerable inconvenience in situations of children who work with their parents, or in other situations where a child spends a good part of the day with his father or mother. It is advisable in such cases for the child to request from the parents "Mehila," meaning, that they waive this obligation to stand, so that he will not be required to stand each and every time the parent enters the room.
Summary: One is obligated to stand each and every time his father or mother enters the room, unless the parent explicitly granted "Mehila," meaning, he/she waived the child’s obligation. If one is standing and knows that his parent will soon be entering the room, he should sit so that he could stand and fulfill the Misva of honoring parents. One must stand when a parent enters even if the parent suffers from a mental disorder and will not notice the display of honor. One who is sitting in a bus, train or airplane must stand when a parent boards.
