Some clinical and etiological aspects of senile dementia of the Alzheimer type (SDA) were elucidated in a case control study of 63 SDA patients and 91 controls. The SDA patients had significantly more commonly both senile and presenile dementia in parents and sibs than the controls. The occurrence of senile dementia in parents or sibs increased the risk for SDA by about 900% when all other relevant factors were taken into account in multiple logistic risk function analysis. The increase of the risk for SDA associated with the occurrence of presenile dementia in sibs was even greater but not statistically significant because of other factors and sample size. There was a negative correlation between the occurrence of hypertension and angina pectoris and SDA, which may be partly due to selective diagnostic criteria of SDA. The beta-globulin fraction of cerebrospinal fluid was significantly reduced in the electrophoresis in the SDA patients compared with the controls.