DNA copy number variation is an important cause of genetic disease. There are several techniques available to detect copy number changes of various sizes, each with their limitations in resolution and cost. Here we outline the development of multiplex amplifiable probe hybridization (MAPH) into a high-throughput diagnostic technique for detecting copy number variation of almost any size. Its application in testing for genetic mutations causing diseases, such as familial breast cancer, Charcot-Marie-Tooth disease Type 1A, Duchenne/Becker muscular dystrophy and familial colorectal cancer is described, as well as its use in identifying chromosomal changes in some individuals with mental retardation. The analysis of the data produced by MAPH is also considered, along with its potential for automation and development of microarray-based MAPH.