Humphrey Bogart, Edward G. Robinson and Claire Trevor had all appeared together in The Amazing Dr. Clitterhouse (1938). In addition, Trevor received her first Oscar® nomination as Bogart's ex-girlfriend in Dead End (1937) and had co-starred with Robinson for five years on the radio series Big City.

The hurricane footage was taken from another Warner Bros. film, Night Unto Night (1949), made before Key Largo but not released until a year later.

When the owner of the Key Largo hotel realized John Huston and Richard Brooks would be staying there for a while, he moved some gaming tables into the place to provide evening entertainment for the men and their wives. Huston loved gambling but rarely won. Before long, director and writer had lost their salaries for the film before they were even paid. Then Huston bet the owner, a Catholic, that he didn't know what the Immaculate Conception was. The owner answered that it was the fact that Christ was born without sin. A quick call to a monsignor in Miami revealed that it was actually the fact that Mary was born without sin. The owner paid them in gambling chips, and Huston won back most of what he had lost. He gave Brooks a few chips, and the writer won back $3,000 of his $8,000 fee.

During filming, Lauren Bacall served tea and cookies to the other actors in her dressing room every afternoon.

Between shots, Lionel Barrymore kept the cast and crew entertained with stories from his career and impromptu musical performances. He would often sing Irish songs with a broad Yiddish accent.

One irony in the casting was that Barrymore, a staunch Republican who hated Franklin Delano Roosevelt, had to deliver a glowing endorsement of everything the New Deal stood for.

Huston named the yacht docked at the hotel pier the Santana, after Bogart's own boat. The actor would later call his production company Santana Pictures.

Memorable Quotes from Key Largo

"Are you thieves or what? You want money? Is this a robbery?"
"Yeah, Pop, we're gonna steal all your towels." -- Lionel Barrymore, as James Temple, and Harry Lewis, as Edward 'Toots' Bass

"After living in the U.S.A. for more than 30 years, they called me an undesirable alien. Me. Johnny Rocco. Like I was a dirty Red or something!" -- Edward G. Robinson, as Johnny Rocco

"I must apologize for Mr. Temple...He doesn't know what he's talking about or who to...Johnny Rocco was more than a king; he was an emperor. His rule extended over booze, slot machines, the numbers racket, and a dozen other forbidden enterprises. He was a master of the fix. Whom he couldn't corrupt he terrified; whom he couldn't terrify, he murdered." -- Humphrey Bogart, as Frank McCloud, interceding for Barrymore, as James Temple

"When Rocco talked everybody shut up and listened. What Rocco said went! Nobody was as big as Rocco. It'll be like that again, only more so! I'll be back up there one of these days and then you're gonna really see something!" -- Robinson, as Johnny Rocco

"You'd give your left arm to nail me wouldn't you? I could see the headlines now, 'Local Deputy Captures Johnny Rocco'. Your picture'd be in all the papers. You might even get to tell on the newsreels how you pulled if off, yeah. Listen hick, I was too much for any big city police force to handle. It took the United States Government to pin a rap on me. And they won't make it stick. You hick, I'll be back pulling strings to get guys elected mayor and governor before you get a ten buck raise." -- Robinson, as Rocco, to John Rodney, as Deputy Clyde Sawyer

"I had hopes once, but I gave them up."
"Hopes for what?"
"A world in which there's no place for Johnny Rocco" -- Bogart, as Frank McCloud, and Robinson, as Rocco

"If there's one thing I can't stand it's a dame who's drunk. They turn my stomach; they're no good to themselves or anybody else. She's got the shakes, see, so she has a drink to get rid of them. It tastes so good she has another one and the first thing you know, she's stinko again." -- Robinson, refusing to give Claire Trevor, as Gaye Dawn, a drink

"My gowns were gorgeous, very décolleté...I wore hardly any makeup, just some lipstick, that's all. No lights, just a baby spot. I wouldn't have any entrance -- they'd play the intro in the dark, the spot would come on and, and there I'd be." -- Trevor, as Gaye Dawn, describing her act

"One Rocco more or less isn't worth dying for!" -- Bogart, as McCloud

"You don't like it, do you Rocco, the storm? Show it your gun, why don't you? If it doesn't stop, shoot it." -- Bogart to Robinson

"A cause isn't lost as long as one person is willing to go on fighting for it." -- Lauren Bacall, as Nora Temple.

"When your head says one thing and your whole life says another, your head always loses." -- Bogart

By Frank Miller