When my father was ill in the hospital a couple of years ago, my sister had P.O.A. over him.
He is now able to care for himself. Is this P.O.A. still valid? Thank you!

Actually rebeldevilo5 is wrong, A POA stays active till it is revoked unless there was a date on it for it to expire.

And a person does not have to be incapable of taking care of thierself,

A POA merely allows another person to sign for another person, in business often a person is given a POA to sign for someone who will be out of town or more, or to do specific business for another person.

So if there was no expiration date on the POA and if he has not revoked the POA it is still in effect.

POA's do end at the death of the person ( this is often confused also) when they do a POA thinking it allows them to take care of their final arrangements. ( not part of the question but general info)