Temperament and attention-deficit/hyperactivity disorder (ADHD) are both typically viewed as biologically based behavioural constructs. There is substantial overlap between ADHD symptoms and specific temperamental traits, such as effortful control, especially in young children. Recent work by Martel and colleagues (2009, 2011) suggests that cognitive control temperamental processes are more closely related to inattention symptoms, whereas stimulus-driven temperamental processes are linked to hyperactivity-impulsivity. The present study tested a model of temperament and ADHD symptoms in typically developing preschoolers and those at risk for ADHD using structural equation modelling. Data were from larger study on ADHD in a short-term longitudinal sample with parent/teacher reports and neurocognitive testing. Participants included 214 preschool children (72.9% male) from diverse ethnic/racial backgrounds and a wide range of socioeconomic status from a large metropolitan center. Cognitive control processes, such as effortful control, but not stimulus-driven processes, are related to inattention "and" hyperactivity. In contrast, stimulus-driven processes, such as emotional reactivity, were related only to hyperactivity symptoms longitudinally. These results suggest that early temperament behaviours and cognitive processes may be indicators of later childhood behavioural difficulties with lasting consequences. (Contains 3 figures and 2 tables.)