Children who begin kindergarten with stronger skills learn faster than do those who enter with lower skills. Minority children tend to enter kindergarten already at a disadvantage, and the gap widens across time. However, little is known about cognitive development among American Indian young children. In this study, 110 American Indian infants from one Northern Plains reservation community were assessed four times between ages 6 months and 36 months, with the Mullen Scales of Early Learning. At 6 months of age, scores were near the national norms; a drop occurred between 6 months and 15 months. Scores then tended to level off below the norms through 36 months. In each domain, we observed a crucial decline over the 1st year of life and relatively little change in the 2nd and 3rd years of life, highlighting the importance of developing culturally syntonic interventions to facilitate cognitive development during the 1st year of life. (Contains 6 figures and 1 table.)