This study aimed to estimate the prevalence and explore the multidimensional complexity of the neuropsychiatric syndromes of AD. Neuropsychiatric symptoms and syndromes of 216 subjects with probable and possible AD diagnosed by NINCDS-ADRDA criteria were evaluated by the Korean version of behavior rating scale for dementia (BRSD-K). The prevalence rate of six neuropsychiatric syndromes (depressive symptoms, inertia, vegetative symptoms, irritability/aggression, behavioral dysregulation, psychotic symptoms) and comorbid neuropsychiatric syndromes were calculated according to the Clinical Dementia Rating scale. To investigate the relationship among neuropsychiatric syndromes, logistic regression analyses were performed. About 95% of patients with AD had one or more neuropsychiatric symptoms and syndromes during the past month. Among the neuropsychiatric syndromes, irritability/aggression (76.2%) was the most frequent, followed by apathy (72.3%) and depressive symptoms (68.0%). About 90% of the subjects had one or more comorbid neuropsychiatric syndromes. The mean numbers of comorbid neuropsychiatric syndromes were significantly varied according to the severity of disease (p<0.05). Depressive symptoms were significantly associated with vegetative symptoms and irritability/aggression (p<0.05). Inertia and psychotic symptoms were significantly associated with vegetative symptoms and behavioral dysregulation, respectively (p<0.05). This study demonstrated that neuropsychiatric syndromes of AD were highly prevalent and involved complex relationships among them.