Identifying infants at elevated likelihood for autism and other developmental differences in the first year of life remains a significant challenge. This study explored associations between behavioral differences in infancy and developmental outcomes in toddlerhood. We conducted a secondary data analysis of 256 infants with an older autistic sibling followed from 6 to 36 months of age. We defined conceptually driven cutoffs for three behavioral measures collected at 6, 9, and 12 months and examined the utility of these measures, individually and in combination, in predicting 36-month outcome classification (typical development or developmental concerns, including autism). Overall, relatively few infants met multiple measure definitions (range: 5 to 43 infants across ages). However, infants meeting multiple definitions had a higher likelihood of developmental concerns outcomes at all ages. Positive predictive values for meeting all three measure definitions combined ranged from 0.67 [0.22, 0.96] at 6 months to 0.95 [0.75, 1.0] at 12 months. These findings suggest that while majority of infants ultimately classified with developmental concerns do not show significant behavioral differences in the first year, when early differences are present, they have predictive value. Combining behavioral tools may help to improve identification of infants most in need of early supports.