Although there have been suggestions that prenatal factors could affect crown dimensions (Bailit and Sung, Archs Oral Biol 13:155-166, 1968; Cohen, Baum, Garn, Osario and Nagy, in: Orofacial Growth and Development, Dahlberg and Graber, eds., Mouton Publishers, The Hague, 1977, pp 119-126), limitations of sample size and investigative design restrict conclusions on the magnitude of the influences. However, using newly-acquired odontometric data on selected participants in the Collaborative Perinatal Project of the National Institute of Neurological and Communicative Disorders and Stroke (NCPP), it is now possible to show systematic effects of three maternal and six developmental conditions on mesiodistal and buccolingual dimensions of both deciduous and permanent teeth. The basic sample consists of 870 white participants studied at the time of their seven-eightyear psychological examinations in 1972 and 1973. They were selected from six cooperating institutions from the Atlantic seaboard and the West Coast (Niswander and Gordon, The Women and Their Pregnancies, D.H.E.W., Washington, 1972). Diabetes, hypothyroidism, and hypertension were the three maternal conditions selected for exploration. Gestation length, birth weight, and birth length were among the fetal or developmental variables studied. The odontometric analyses primarily involved the permanent incisors, first molars and deciduous cheek teeth (dc through dm2). A group of clinically normal children was also included for comparison, since single-source odontometric standards for deciduous and permanent teeth did not exist at the time the project was conceived. Mean crown dimensions of the normal NCPP group proved to be virtually indistin-