The 70 infants who survived birth weights of 1,500 gm (3 lb 5 oz) or less at the Chicago Lying-In Hospital between 1952 and 1956 with controls matched for obstetric, social, and economic factors were recalled for physical, neurologic, audiometric, ophthalmologic, and psychometric examinations approximately ten years after birth. Data were obtained from 65 (93%) of the complete pairs: 70% of these at the University of Chicago, 20% by comparable examination centers elsewhere, 10% through reports. Through analysis, mainly by intrapair differences, it was determined that the controls and prematures matched on a wide range of medical, socioeconomic, and obstetric parameters other than low birth weight. Prematures exceeded their controls in mortality, mental retardation, poor school performance, pyramidal tract disorders, and visual defects. The data are stored on cards and magnetic tape for additional analysis.