Intrauterine growth retardation, or being small for gestational age (SGA), has a life-long impact on a fetus's potential for development and survival. The incidence and relative risk of short stature in children born SGA were studied using a Swedish healthy full-term (37-43 wk of gestation) singleton birth cohort (n = 3650) from Göteborg, followed from birth to final height at about 18 y of age. Most infants, defined as SGA on the basis of a birth length less than -2 standard deviation scores (SDS) below the mean (SGAL infants), showed catch-up growth during the first 6 mo after birth, and by 1 y only 13.4% of the SGAL infants were below -2 SDS in height. This percentage decreased further during childhood to reach a value of 7.9% at 18 y of age. Although most SGAL infants have catch-up growth in early life, those who do not constitute 21% of short, prepubertal children. At 18 y of age, 22% of the total short population were short at birth (< -2 SDS), whereas when birth weight was used to define SGA, only 14% of the 18-y-old short population were light at birth. SGAL infants were found to have a 7-fold higher risk for short final stature (relative risk, 7.1; 95% confidence interval, 3.7-13.6) in comparison with the non-SGAL group. In a multiple linear regression analysis, both birth length and mid-parental height were found to be significantly related to the magnitude of catch-up growth from birth to 18 y of age. Neither the length of gestation nor birth weight showed such a relationship. It is concluded that the vast majority (> 86%) of "healthy" full-term singleton SGAL infants will achieve catch-up in height during the first 6-12 mo of life, and that this is almost independent of whether birth weight or birth length is used to define SGA. Of the remaining, non-catch-up SGA infants, about 50% remain short in final height, and thus constitute a high risk group for persistent short stature.