Being born small for gestational age (SGA) in length is a sign of growth failure due to malnutrition in pregnancy or other serious disorders. In previous publications it was shown that SGA born neonates may experience a compensatory growth spurt (catch-up growth) in infancy and childhood (Olbertz et al. in press). The timing of this growth spurt, however, was not well described. We analyzed longitudinal data of 5,138 SGA infants and children, collected by licensed physicians in Germany and centrally stored in the Database Management System of CrescNet at the University of Leipzig. We confirm that SGA born infants undergo a catch-up in height SDS after birth and up to 2 years of life. 2,712 SGA newborns out of 2,846 showed catch-up in length SDS. The catch-up occurred already during the 4th to 16th postnatal weeks. We analyzed infants who did not show a catch-up within this time period, or even had a loss in height SDS. These infants have a significant lower height SDS throughout the first 5 years after birth and especially in the timeframe of 60th to 64th month after birth (-1.33 mean height SDS in catch-up group, -2.49 in non-catch-up group, p-value < 0.001, CI = [0.827, 1.483]). Even though the medical reasons for the lack of catch-up growth in young SGA infants may not be known, absence of this catch-up within the 4th to 16th postnatal week can be used to early identify SGA infants with high risk of growth failure within the following 5 years.