We studied the fetal and maternal characteristics that affect the diagnosis of intrauterine growth retardation and lead to variations in the sensitivity, specificity and predictive values. The population comprised the 18,166 women who consulted and delivered in two teaching hospitals in Paris from 1978 to 1983. Specificity was lower when a child was born before 37 weeks, with a small weight-for-gestational age, and when the mother had experienced complications during either her obstetric history or current pregnancy. Conversely, sensitivity was higher when these maternal and fetal characteristics were present. Positive predictive values rose in the presence of a risk factor for small-for-dates, but the rise was smaller than would have been expected if sensitivity and specificity had remained at the levels observed in the low-risk group.