Objective: Ideomotor apraxia was studied in patients with Alzheimer disease (AD) and unilateral left hemispheric damaged (LHD) stroke to determine whether these groups differed. Background: Given that the neuropathology of AD is bilateral and more diffuse than the localized involvement in patients after an LHD stroke, and given that the cognitive deficits in AD are more widespread than in LHD stroke, the authors predicted that patients with these disorders would differ in response to an auditory command task administered to evaluate ideomotor apraxia, and that the two patient groups would be significantly more impaired than healthy matched control subjects. Methods: Twenty-one persons were studied, including equal numbers of patients with AD, patients with unilateral LHD stroke, and control subjects. An auditory command test of limb apraxia was administered and videotaped to score performance and to code spatial-temporal or content errors. Results: The patients with AD and LHD stroke were significantly more impaired than healthy control subjects. Whereas the patients with AD and LHD stroke were equally apraxic and did not differ in their performance of transitive limb movements, the patients with AD were significantly more impaired than the patients with stroke when performing intransitive limb movements. A positive correlation was found between severity of dementia and severity of apraxia in the patients with AD. The patients with LHD stroke were as likely to make spatial-temporal as content errors when performing intransitive limb movements, whereas the patients with AD made content errors only. Error types produced with transitive limb movements did not differ between groups; spatial-temporal errors were the most common errors made both by patients with AD and patients with LHD stroke. Conclusions: As predicted, patients with AD and with LHD stroke were impaired when producing limb movements after auditory command, and both patient groups were significantly more impaired than the healthy adults. Patients with AD were significantly more impaired than patients with stroke when performing intransitive limb movements, and error types differed by group. Patients with AD and patients with stroke were equally impaired when performing transitive movements, and error types did not differ by group. Patients with ideomotor apraxia are often degraded in their production of transitive and intransitive movements, and the observation that performance may differ depending on the type of limb movement suggests that movement representations for transitive and intransitive movements may be at least partially independent.