(It's always nice to put good news out there about the US!---Lori)
He told them: "Write any amount you like - I'm good for it."
The couple took him at his word to the tune of $100,000, about £50,600, reports the Daily Mirror.
But they could not believe their luck when the cheque cleared.
The couple met their elderly benefactor in Dr Salami's Cafe in Pella, Iowa. He first asked if they had any kids. They told him they had a two-year-old.
Then he gave his conditions: They were to use the cash to buy a house, never reveal his identity - nor their own full names. And they have to name their next child after him.
Alissa and Barry thought it was probably a joke but decided to play along by filling in the amount for $100,000.
Barry said: "We decided to give it a whirl next day, never thinking he was serious - but he was!"
The mystery man also left the waitress a $100 tip.
She said: "He is just a nice guy. You never know who is sitting next to you. You never know when you can make a difference to someone else's life."