Study to Determine Whether There Are Any Cognitive or Motor Effects From Taking the Medicine Risperidone.

Inclusion Criteria: * Aged 4 to 14 years, inclusive * Male or female gender * Reason for receiving risperidone must include severe conduct problems * Received risperidone treatment for at least 4 months * Dosage in the range of 0.01 to 0.099 mg/kg/day * Capable of discontinuing risperidone for up to 14 days in the judgement of child's physician * Taking co-therapy with psychostimulants, antihistamines, melatonin, and chloral hydrate is allowed as long as co-therapy is held constant * Taking co-therapy for sleep with guanfacine hydrochloride, clonidine hydrochloride, and trazodone hydrochloride is allowed so long as co-therapy is held constant * Must have a reliable adult carer who can report on subject's behavior and attend scheduled assessments * Parent or guardian must give informed consent, and subject must give assent if 14 years of age or older * Must be considered physically healthy on the basis of physical exam and medical history. Exclusion Criteria: * Patients who meet DSM-IV criteria for schizophrenia, schizophreniform disorder, dissociative disorder, major depression, schizoaffective disorder, substance induced psychotic disorder * Subjects who are pregnant * Subjects with known seizure disorder * Subjects with a history of neuroleptic malignant syndrome * Subjects with a known or suspected history of severe drug allergy or hypersensitivity * Subjects must have no significant medical disease * Subjects must not be taking any other psychotropic medications.