Combine Old Bay Seasoning, salt, and pepper; stir well, and set aside.
Combine equal parts of water and vinegar in a large stock pot with a steaming rack to a level just below the rack. Bring water-vinegar mixture to a boil. Add a layer of crabs; sprinkle with seasoning mixture. Repeat layers. Cover and steam 20 minutes or until crabs turn red in color. Drain, and serve the crabs immediately.