Being born small for gestational age (SGA) is considered a developmental vulnerability. Alternatively, SGA may be viewed as a marker for individual susceptibility to environmental experiences. The aim was to test if individuals born SGA are more susceptible to both negative and positive environmental experiences assessed by sensitive parenting in childhood compared with those born appropriate for gestational age (AGA). The target outcome was wealth in young adulthood. A total of 438 participants (SGA, n = 109; AGA, n = 329) were studied as part of the prospective Bavarian Longitudinal Study of neonatal at-risk children. Maternal sensitivity was observed during a standardized mother-child interaction task, and IQ was assessed with the Kaufman Assessment Battery for Children at age 6 years. At age 26, participants' wealth was assessed with a comprehensive composite score. Individuals born SGA were found to be more susceptible to the effects of sensitive parenting after controlling for gestational age and IQ at age 6 years. When maternal sensitivity was lower than average, SGA adults did worse than AGA adults, but when exposed to above-Average maternal sensitivity in childhood, they obtained significantly higher wealth than their AGA peers by 26 years of age.