Background: "With Significant Callous-Unemotional Traits" has been proposed as a specifier for conduct disorder (CD) in the upcoming revision of the Diagnostic and Statistical Manual of Mental Disorders (DSM-V). The impact of this specifier on children diagnosed with CD should be considered. Methods: A multi-site cross-sectional design with volunteers (n = 1136) in the third-seventh grades and 566 consecutive referrals (ages 5-18) to a community mental health center were used to estimate the prevalence rates of CD with and without the proposed specifier. In addition, the degree of emotional and behavioral (especially physical aggression) disturbance and level of impairment in youth with and without CD and with and without the specifier was evaluated. Results: In the community sample, 10%-32% of those with CD and 2%-7% of those without CD met the callous-unemotional (CU) specifier threshold depending on informant. In the clinic-referred sample, 21%-50% of those with CD and 14%-32% without CD met the CU specifier threshold depending on informant. Those with CD and the specifier showed higher rates of aggression in both samples and higher rates of cruelty in the clinic-referred sample. Conclusions: Results indicate between 10% and 50% of youth with CD would be designated with the proposed CU specifier. Those with CD and the specifier appear to be more severe on a number of indices, including aggression and cruelty.