A 6-week randomized, double-blind, placebo controlled trial of desipramine (DMI) in daily doses averaging 4 to 5 mg/kg for the treatment of children and adolescents with attention deficit disorder with hyperactivity (ADDH) was further analyzed. Investigators examined whether comorbidity of ADDH with conduct disorder, major depression, an anxiety disorder, or a family history of ADDH predicted response to DMI treatment. There was a highly significant effect of treatment with DMI in outcome assessments, but responses to DMI were indistinguishable in ADDH patients with and without a comorbid disorder or familial ADDH. Cases of "pure" ADDH (lacking comorbidity with depression, anxiety, or conduct disorder and having a positive family history of ADDH) showed a trend toward lesser placebo responses and a corresponding greater DMI-placebo difference. These findings suggest that (1) DMI is effective in simple, noncomorbid cases, (2) DMI is not selective for comorbid cases, but (3) a response to DMI can be obtained even in complex cases of ADDH with associated comorbidity.