Empirical studies have documented a variety of social abnormalities in infancy that indicate risk for later social and behavioral difficulties. There is very little research illustrating the presence of such behavioral vulnerabilities with frequent repeated measures, and the feasibility of designing interventions for improving social engagement in infants less than 1 year of age. In the context of a multiple baseline research design, three young infants, ages 4, 7, and 9 months, referred for concerns about social engagement were assessed for affect, social interest, eye contact avoidance, and response to name. In addition, the feasibility of implementing an intervention to target social behaviors was examined. Results demonstrated that (a) consistently low or erratic levels of social behavior were evident throughout the baseline assessment period, (b) these patterns could be improved with a brief intervention (a modified Pivotal Response Treatment) showing an immediate increase and stability of social engagement, and (c) social engagement remained at a stable and high level at follow-up. The results are discussed in terms of implications of early assessment and intervention for clinical populations, including infants with autism spectrum disorder.