ABSTRACT The Conners' Continuous Performance Test (CPT) is a neuropsychological task that has repeatedly been shown to differentiate ADHD from normal groups. Several variables may be derived from the Conners' CPT including errors of omission and commission, mean hit reaction time(RT), mean hit RT standard error, d', and beta. What each CPT parameter actually assesses has largely been based upon clinical assumptions and the face validity of each measure (e.g., omission errors measure inattention, commission errors measure impulsivity). This study attempts to examine relations between various CPT variables and phenotypic behaviors so as to better understand the various CPT variables. An epidemiological sample of 817 children was administered the Conners' CPT. Diagnostic interviews were conducted with parents to determine ADHD symptom profiles for all children. Children diagnosed with ADHD had more variable RTs, made more errors of commission and omission, and demonstrated poorer perceptual sensitivity than nondiagnosed children. Regarding specific symptoms, generalized estimating equations (GEE) and ANCOVAs were conducted to determine specific relationships between the 18 DSM-IV ADHD symptoms and 6 CPT parameters. CPT performance measures demonstrated significant relationships to ADHD symptoms but did not demonstrate symptom domain specificity according to a priori assumptions. Overall performance on the two signal detection measures, d' and beta, was highly related to all ADHD symptoms across symptom domains. Further, increased variability in RTs over time was related to most ADHD symptoms. Finally, it appears that at least 1 CPT variable, mean hit RT, is minimally related to ADHD symptoms as a whole, but does demonstrate some specificity in its link with symptoms of hyperactivity.