The pattern of hearing loss of children in schools for the deaf provides little information regarding etiology, but it is possible to evaluate the relative contribution of several etiologic factors by study of medical histories and family records. Traits such as thyroid or pigment anomalies can be used to identify particular genetic defects in a small proportion of deaf children; however, family data suggests that over half of all cases are the result of inheritance. Although most of the responsible genes are not now recognizable, pedigree data give excellent fit to simple genetic models. Thus we are able to estimate the minimum number of genes causing deafness and predict risks of deafness in offspring. Using experimental animals with patterns of hereditary deafness similar to man we can observe development and anatomy which suggest important directions for the study of deaf children.