A brief assessment of cognitive and motor functions associated with the frontal/subcortical system was evaluated for discriminant validity. Patients with dementia of Huntington's disease and Parkinson's disease performed as well as normal control subjects on the Mini-Mental State Exam (MMSE) but significantly worse on the Frontal/Subcortical Assessment Battery (FSAB). Discriminant function analyses yielded significantly higher rates of accurate classification with FSAB and MMSE combined than with MMSE alone. Patients with Alzheimer's disease scored significantly lower than other groups on both measures. The authors recommend the FSAB as an adjunct to the MMSE for brief assessments of patients with suspected frontal or subcortical pathology.