We report three related studies of covert visual spatial orienting in child attention deficit hyperactivity disorder (ADHD). In Study 1, we examined covert visual spatial orienting in ADHD and comparison boys, Study 2 comprised a dose-response study of methylphenidate for the ADHD group, and Study 3 was an investigation of biological and adoptive parents. In contrast with comparison subjects (n = 17). ADHD boys aged 6-12 (n = 27) showed both slower reaction times overall and within-condition (lateral) asymmetries in reaction times. Specifically, boys with ADHD reacted more slowly to uncued targets in the left visual field than in the right visual field. Responses to stimuli in the two visual fields were differentially affected by methylphenidate for the ADHD group. Medication equalized visual field responses to the uncued targets, resulting in a significant cue x dose x visual field interaction. Further, medication altered the relative cue responsivity in the two visual fields, resulting in a significant dose x visual field interaction for the Validity Effect. Biological parents of ADHD boys (n = 16) also showed slower reaction times to uncued left visual field targets than to right visual field targets; in addition they showed slower response to invalidity cued targets in the right visual field. These literal effects were not observed in adoptive parents of ADHD boys (n = 12) or biological parents of comparison boys (n = 14). Possible abnormal hemispheric asymmetry of attention functions in boys with ADHD and their biological parents is discussed.