We have been assessed menntal functions and activities of daily life (ADL) of 878 dementia patients(279 men and 599 women) for 15 years using ND %scale(Nishimura Dementia scale), NM scale(Nishimura behavioral scale for the mental state), N-ADL(Nishimura behavioral scale for ADL) and Hashegawa dementia scale.Of these cases, 185 demented patients (54 men and 131 women) have been followed up over three years using ND scale, NM scale and N-ADL every year or every six months. Studied patients consist of 98 patients of Alzheimer type dementia (ATD) (25 men and 73 women), 69 patients of cerebral vascural dementia (CVD) (21 men and 48 women) and 18 patients of mixed type dementia and other dementia (8 men, 10 women).Differences of the change of mental functions are found between the patients of ATD and CVD. The mental functions of the patients of ATD have been linearly and gradually missing, while those of the patients of CVD have not. Differences of ADL are also found between them.At the early stage of ATD, the missing rate of mental functions can be slower if the patients have suitable care and treatment. The ATD patients of slow progress of dementia have good families and his or her reasons for living, and have not been left alone in their daily life.