US religious broadcaster Pat Robertson has told viewers of his 700 Club television show that divorcing a spouse with Alzheimer's disease is justifiable because the disease is "a kind of death".

During the portion of the show where the one-time Republican presidential candidate takes questions from viewers, Robertson was asked what advice a man should give to a friend who began seeing another woman after his wife started suffering from the incurable neurological disorder.

Pat Robertson.

"I know it sounds cruel, but if he's going to do something, he should divorce her and start all over again, but make sure she has custodial care and somebody looking after her," Robertson said.

The chairman of the Christian Broadcasting Network, which airs the 700 Club, said he wouldn't "put a guilt trip" on anyone who divorces a spouse who suffers from the illness, but added, "get some ethicist besides me to give you the answer".