The relations of childhood fearfulness (observed and adult reported) and adult-reported shyness at 18 (n = 256) and 30 (n = 230) months of age were assessed. Fear was positively related to shyness concurrently and longitudinally, but slightly more consistently at 18 months. The moderating roles of observed maternal sensitivity and children's sex in the relation between 18-month fearfulness and 30-month shyness, and between 18- and 30-month shyness, were tested. The positive relation between mother-reported fearfulness and shyness was strongest for sons of insensitive mothers but was not significant for daughters of sensitive, average, or insensitive mothers. The positive relation between mother-reported 18- and 30-month shyness was strongest for sons of insensitive mothers and for daughters of sensitive mothers. Moreover, when using scores of fear or shyness that were independent of each other, 18-month mother-reported fearfulness continued to interact with sex and sensitivity to predict 30-month shyness; however, the positive relation between Time 1 and Time 2 shyness was consistent across sex and levels of sensitivity.