Objective: When behavioral problems resulting from attentional difficulties present, often in preschool, it is unknown whether these problems represent preexisting altered brain development or new brain changes. This study examines whether infant sensory gating of auditory evoked potentials predicts parent-reported behavior at 40 months. Method: P50 sensory gating, an auditory evoked potential measure reflective of inhibitory processes in the brain, was measured in 50 infants around 70 days old. Parents, using the Child Behavior Checklist, reported on the child’s behavior at 40 months. Results: Controlling for gender, infants with diminished sensory gating had more problems later with externalizing behavior (F = 4.17, ndf = 1, ddf = 46, p = .047), attentional problems (F = 5.23, ndf = 1, ddf = 46, p = .027), and anxious/depressed symptoms (F = 5.36, ndf = 1, ddf = 46, p = .025). Conclusion: Diminished infant P50 sensory gating predicts attention symptoms 3 years later. These results support the hypothesis that preschool attentional dysfunction may relate to altered brain development that is detectable years prior to symptom onset. (J. of Att. Dis. 2013; XX(X) 1-XX)