Intrauterine growth retardation (IUGR) may affect up to 10% of pregnancies and results in substantially increased perinatal morbidity and mortality. Although many infants are small on a constitutional basis and not as a result of disease, many others suffer malnutrition from chronic progressive uteroplacental insufficiency. Genetic disease, embryonic infection, and various drug exposures may also result in IUGR. Inconsistency of diagnostic criteria has seriously hampered clinical research aimed at clarification of both the short- and long-term implications of IUGR. This part of the report examines both the significance and clinical definition of IUGR and reviews the diagnostic tests used for the detection of the problem of impaired fetal growth. The clinical approach to the management of IUGR is presented in the subsequent part of the report, which includes the ultrasonic evaluation and management of this entity.