Data on public fallout shelters in the United States, as listed by location, size, type and degree of protection in the National Shelter Survey, were combined with census data on basements in private residences. An algorithm based on distance to shelter, quality of public shelters, and use of home basements was devised to simulate the probable distribution of the U.S. population in shelters near their homes. Under the most favorable conditions only about half the population could find space in public shelters. Home basements have the potential to shelter many other people, but in some shelterdeficient counties other fallout shelter must be provided. Number of occupants and protection quality of the shelters used is also examined. Possible solutions to the shortage of adequate, accessible shelter are examined.