Postnatal growth of 724 (423 premature, 301 full-term) small for gestational age infants (SGA, birth length less than the third length percentile (P3) for gestational age) was studied for the first 2 y of life. The study group consisted of all SGA infants who had been admitted over a period of 8 y at the Departments of Neonatology of three University Hospitals in The Netherlands with exclusion of infants with well defined causes for growth retardation, such as chromosomal disorders, syndromes, severe malformations, or complications during the neonatal period or later on. The aim of the study was to describe postnatal growth of SGA infants and to find predictive factors for catch-up growth > or = P3 during the first 2 y of life. The majority (around 85%) of the healthy SGA infants showed catch-up growth to a height > or = P3 during the first 2 y of life. The percentage of premature SGA infants with catch-up growth > or = P3 at 2 y of age (82.5%) was not significantly different from that of full-term SGA infants (87.5%). Birth length SDS was more sensitive than birth weight SDS in predicting catch-up > or = P3 in premature SGA infants. In contrast, birth weight SDS was the best predictor for catch-up > or = P3 in full-term SGA infants. Gestational age, multiple birth, and sex were not significantly associated with catch-up in height > or = P3.(ABSTRACT TRUNCATED AT 250 WORDS)