Summary The present article reviews some ofthe ways a knowledge of medical genetics can be of practical value to the pediatrician. 1. The patterns of simple mendelianinheritance are described, as seen in the human pedigree. 2. The technique of taking the familyhistory is discussed. It is suggested that the family history should routinely contain (a) a statement regarding the occurrence in the patient's family of diseases relevant to the patient's complaints, (b) a record of the patient's parents and siblings and (c) a statement about whether the patient's parents are “blood relatives” (parental consanguinity). 3. The problems of counseling in medical genetics are discussed, particularly in relation to the question of whether the parents of a child with a genetically influenced disease should have further children. 4. A list of pediatric diseases is presented, with a summary of what is known of the genetics of each disease.