Current clinical diagnostic techniques for the detection of small duplications and deletions include microscopic cytogenetics with Giemsa banding and FISH. An alternative approach is to use genetic markers, to detect duplications and deletions. The application of this technique to the entire genome as a test for segmental aneusomy requires a method for selecting a panel of markers that could be used and an estimate of the statistical power. We have developed a computer program, DECIDE, that performs these tasks. Given an input map of markers, DECIDE generates a near optimal list of markers and estimates the probability of detecting monosomy or trisomy of varying physical size. We demonstrate the program on a large map of markers obtained from the Southampton and CEPH databases. We conclude that this approach to screening for duplications and deletions is theoretically possible and would have a power comparable to routine Giemsa-banded chromosome analysis.