The present study examined the genetic and environmental etiology of decision-making (Iowa Gambling Task; Bechara, Damasio, Damasio, & Anderson, 1994), in a sample of twins at ages 11-13, 14-15, and 16-18 years. The variance across five 20-trial blocks could be explained by a latent "decision-making" factor within each of the three times of IGT administration. This latent factor was modestly influenced by genetic factors, explaining 35%, 20% and 46% of the variance within each of the three times of IGT administration. The remaining variance was explained by the non-shared environment (65%, 80% and 54%, respectively). Block-specific non-shared environmental influences were also observed. The stability of decision-making was modest across development. Youth showed a trend to choose less risky decks at later ages, suggesting some improvement in task performance across development. These findings contribute to our understanding of decision-making by highlighting the particular importance of each person's unique experiences on individual differences. (Contains 3 tables and 4 figures.)