The probability of detecting sites using subsurface testing programs is a serious concern for archaeologists working in the eastern United States. Some have suggested that current test-probe programs provide a poor method for estimating the frequency and distribution of sites. This article examines the usefulness of subsurface testing programs by comparing the results of an Eastern subsurface survey with a pedestrian surface survey conducted in the Southwest. The subsurface survey at Shelter Island, New York, was designed so that probability limits could be calculated for detecting sites of varying sizes. These probabilities were then employed to estimate the number and kinds of sites contained in sample units. When these results were compared with those from a pedestrian surface survey in northeastern Arizona, the results suggested that carefully designed subsurface surveys, although extremely labor-intensive, can provide settlement-pattern information as detailed as that collected in surface surveys.