Little is known about slow-to-warm-up temperament in infancy. This study examined the trajectory of shyness in children who were slow-to-warm-up in infancy in comparison to children with other temperament profiles in infancy. Participants were 996 mothers and children in the NICHD SECC studied from 6 months to first grade. Latent growth curve modeling showed that children who were slow-to-warm-up in infancy tended to be shy in early childhood, but with increasing age these children became indistinguishable from children who were easy or intermediate. In comparison, children who were difficult in infancy remained more shy than children with other temperament profiles. Maternal sensitive and stimulating/supportive parenting was associated with less shyness in early childhood for boys who were slow-to-warm-up in infancy. Findings support the distinctiveness of the slow-to-warm-up temperament in comparison to other temperament profiles as well as its potential usefulness for predicting later child outcomes. (Contains 4 tables and 3 figures.)