Objetive: The study aimed to describe the prevalence and severity of neuropsychiatric symptoms in patients with Alzheimers disease (AD) and vascular dementia (VaD). Patients and methods: We prospectively studied 65 patients with dementia, 37 met the criteria of NINCDS-ADRDA for probable AD and 28 the clinical and radiological criteria of NINDS-AIREN for VaD. Among VaD patients, 22 met the radiological criteria for subcortical VaD. The Minimental State Examination (MMSE) and the Neuropsychiatric Inventory (NPI) were used to evaluate cognitive and neuropsychiatric symptoms. All patients underwent a neuroimaging study (CT scan and/or MRI). Patients were not treated with antidementia or psychotropic drugs. Results: Age, gender, educational level and MMSE scores did not differ between patients (p > 0.05). The total prevalence of neuropsychiatric symptoms was similar in both groups (AD 94.6% vs. VaD 96.4%, p= 0.727). Sleep disturbances (35.1% v 3.6%, p =0.002) and appetite changes (37.8% v 14.3%, p = 0.032) were more prevalent in AD patients than in VaD patients who met the NINDS-AIREN criteria. Sleep disturbances (35.1% v 4.5%, p=0.008), appetite changes (37.8% v 13.6%, p = 0.047) and aberrant motor behaviour (24.3% v 0%, p =0.012) were more prevalent in AD patients than in subcortical VaD. The total scores for sleep disturbance, appetite changes and aberrant motor behavioural were higher in AD patients (p < 0.05). Conclusions: There were no significant differences between AD and VaD patients, except that sleep disturbances, appetite changes and aberrant motor behaviour that were more prevalent and severe in AD.