Genetic linkage analysis is a powerful tool to detect the chromosomal location of disease genes. It is based on the observation that genes that reside physically close on a chromosome remain linked during meiosis. For most neurologic diseases for which the underlying biochemical defect was not known, the identification of the chromosomal location of the disease gene was the first step in its eventual isolation. By now, genes that have been isolated in this way include examples from all types of neurologic diseases, from neurodegenerative diseases such as Alzheimer, Parkinson, or ataxias, to diseases of ion channels leading to periodic paralysis or hemiplegic migraine, to tumor syndromes such as neurofibromatosis types 1 and 2.