Background: The aim of the present study was to investigate how three different types of inhibitory control--interference control within task, interference control outside task, and prepotent response inhibition--and two types of working memory--verbal and spatial--would relate to early symptoms of attention deficit/hyperactivity disorder (ADHD) and oppositional defiant disorder (ODD), both concurrently and longitudinally. Methods: Seventy-two preschoolers, 1/3 who had been identified as being at risk for developing ADHD and/or ODD, completed neuropsychological tasks designed to measure inhibitory control and working memory. Behavioral symptoms were measured through parental and teacher ratings of the DSM-IV criteria for ADHD and ODD. Results: Our results suggest distinct types of inhibitory control as being good predictors of concurrent and longitudinal symptoms of ADHD, rather than ODD. However, no associations were obtained between working memory and ADHD or ODD symptoms either concurrently or longitudinally. Conclusions: This study emphasizes the need to isolate complex executive processes and break them down into components in order to properly understand the neuropsychological roots involved in ADHD and ODD.