Objective: To examine the relationship between time reproduction, performance variability, and sustained attention deficits in children with attention-deficit/hyperactivity disorder (ADHD) combined (ADHD-C) and inattentive (ADHD-I) subtypes, relative to matched controls. Method: Participants (age range 7.1-14.1 years) performed a time reproduction task. A subset of the ADHD group was also tested on the Sustained Attention to Response Test. Absolute discrepancy, accuracy coefficient, and intraindividual variability scores on the time reproduction task were compared across the three groups (ADHD-C: N = 20; ADHD-I: N = 19; controls: N = 44) and correlated with the Sustained Attention to Response Test. Results: First, significantly better performance was observed in matched controls than in children with ADHD on the time reproduction task. Second, there was a significant difference between the two ADHD subtypes in the variability of the size of errors made at high time intervals (36-60 seconds). Third, intraindividual performance variability in the direction (over- versus under-estimations) of time reproductions correlated with sustained attention performance. Conclusions: Children with ADHD varied more in the size and direction of their time reproduction errors than control children. Those with ADHD-C demonstrated more intraindividual variability than did those with ADHD-I in the size of their errors. The data provide support for a relationship between sustained attention and time reproduction. This relationship has previously been inferred from common right-lateralized neural circuitry that is thought to subserve these processes.