Encopresis and attentional dysfunction are common neurobehavioral disorders of childhood. The extent to which these disorders occur in association is unknown. The purpose of this study is to document the comorbidity of attentional dysfunction in a clinically identified population of encopresis patients. We used the Child Behavior Checklist (CBCL) to estimate the prevalence of disordered attention or hyperactivity in a group of children with encopresis seen at a tertiary care facility. Responses to CBCL questionnaires were analyzed to compare scores on the "hyperactive" behavior subscale with published normative data. The number of encopretic respondents with T scores above 70 (> 2 SD above the mean) on a hyperactivity subscale was ascertained for each age and gender cohort. From 347 eligible new clinic patients, responses from 167 were suitable for analysis. Overall, 23.4% of children with encopresis (95% confidence interval: 17.2%-30.5%) had T scores on the hyperactive subscale higher than 70. This prevalence (ten fold greater than expected in the normal population) was similar in both genders and across age groups. This association between attentional dysfunction and encopresis has significance for theories regarding etiology and for practical treatment strategies.