We examined associations between child inhibitory control, harsh parental discipline and externalizing problems in 120 4 year-old boys and girls in the US, China, and Japan. Individual differences in children's inhibitory control abilities, assessed using behavioral tasks and maternal ratings, were related to child externalizing problems reported by mothers. As predicted, both child inhibitory control and maternal harsh discipline made significant contributions to child externalizing problems in all three countries. Across countries, child inhibitory control and maternal harsh discipline made significant "independent" contributions to early externalizing problems, suggesting an additive model of association. Our findings supported the cross-cultural generalizability of child inhibitory control and parental harsh punishment as key contributors to disruptive behavior in young children.