A deranged son fatally stabbed his 71-year-old father tonight in their Upper West Side home before trying to take his own life, cops said.

The 33-year-old man plunged the knife into his dad’s neck around 7:15 p.m. inside the 31st-floor apartment on West 87th Street, officials said.

He then slashed his own wrists in a failed suicide attempt.

It wasn’t immediately clear what sparked the bloodshed.

The father died in the apartment and the son was rushed to St. Luke’s Hospital where he was listed in stable condition.

Charges were pending.