The current study examines the combined effects of temperamental activity and shyness on the growth in children’s internalising problems from infancy to middle childhood. Participants were n = 921 parents from a population-based longitudinal sample in Norway. Mothers reported child temperamental traits and internalising problems when children were 1.5, 2.5, 4.5, and 8.5 years old. Shyness (but not activity) was found to predict increased internalising behaviour across all time points. Temperamental interaction effects were also observed and activity level appeared to act as a protective factor in the development of internalising problems for shy boys, but not for shy girls. Results are discussed in terms of gender-specific relational mechanisms and processes that may occur between infancy and 8.5 years of age.