Associations between emotional responses to maternal separation and cognitive performance were expected to change with cognitive development over the first year. In this longitudinal study of 39 infants, measures of separation and reunion distress at 2, 6, and 10 months were interleaved with measures of sensorimotor coordination at 4, 8, and 13 months. Separation distress at 2 months predicted lower sensorimotor scores, whereas separation distress at 6 and 10 months corresponded with higher scores. Duration of distress in reunion showed the same pattern of associations, when controlled for general emotionality Infants' positive engagement and physical touch with their mothers at 10 months predicted higher sensorimotor scores as well. Emotional responses and cognitive performance may be linked by individual differences in self-regulation and attentional engagement, as mediated by age-specific developmental issues.