We investigated the development of ego-control (EC) and ego-resiliency (ER) over a 13-year period in a cohort of Swedish children first assessed at 2 years of age. Children became more ego-controlled over time although individual differences in EC remained stable. Children's levels of resiliency increased from 2 to 3 years of age and then declined when they were 7 and 8 years of age. Boys continued to become less resilient in adolescence whereas girls became more resilient. Individual differences in boys' resiliency levels were more stable over the 13-year span than girls'. The inter-correlations between EC and ER were only significant for boys at 2 and 15 years of age. The external validity of EC and ER was demonstrated by significant associations with ratings of the children's adaptation to school as well as with their measures of their internalizing and externalizing behavior problems. (Contains 3 tables and 2 figures.)