To emphasize the importance of clinical and ultrastructural findings for diagnosing adult neuronal ceroid lipofuscinosis (ANCL), the authors retrospectively reviewed six patients with biopsy-proven ANCL. In all cases, ophthalmologic examinations were normal, and electron microscopic studies demonstrated characteristic granular osmiophilic deposits within the eccrine epithelial cells. The inheritance and mechanism of ANCL remain unknown, and the diagnosis is based on clinical features and ultrastructural examination of the cerebral tissue or extracerebral accumulation of lipopigments. This study suggests that ANCL should be considered as a possible diagnosis in patients with early-onset dementia.