The main game revolves around the opening of a set of numbered briefcases, each of which contains a different prize (cash or otherwise). The contents (i.e., the values) of all of the cases are known at the start of the game, but the specific location of any prize is unknown. The contestant claims (or is assigned) a case to begin the game. The case's value is not revealed until the conclusion of the game.

The contestant then begins choosing cases that are to be removed from play. The amount inside each chosen case is immediately revealed; by process of elimination, the amount revealed cannot be inside the case the contestant initially claimed (or was assigned). Throughout the game, after a predetermined number of cases have been opened, the "Banker" offers the contestant an amount of money and/or prizes to quit the game; the offer is based roughly on the amounts remaining in play and the contestant's demeanor, so the bank tries to 'buy' the contestant's case for a lower price than what's inside the case. The player then answers the titular question, choosing:

"Deal", accepting the offer presented and ending the game, or
"No Deal", rejecting the offer and continuing the game.

This process of removing cases and receiving offers continues, until either the player accepts an offer to 'deal', or all offers have been rejected and the values of all unchosen cases are revealed. Should a player end the game by taking a deal, a pseudo-game is continued from that point to see how much the player could have won by remaining in the game. Depending on subsequent choices and offers, it is determined whether or not the contestant made a "good deal", i.e. won more than if the game were allowed to continue.

Since the range of possible values is known at the start of each game, how much the banker offers at any given point changes based on what values have been eliminated (i.e. the offer increases if lower values are eliminated and decreases if upper values are eliminated). To promote suspense and lengthen games, the banker's offer is usually less than the expected value dictated by probability theory, particularly early in the game.[2] Generally, the offers early in the game are very low relative to the values still in play, but near the end of the game approach (or even exceed) the average of the remaining values.