Subjects with mild cases of senile dementia of the Alzheimer type (SDAT n = 18) were followed up over four years with 16 behavioral tests given during four test periods. This group was compared with a normal group (n = 30) matched on age (64 to 81 years), sex, and socioeconomic status. Each of the 16 tests reflected significant group differences, with the normal subjects showing little or no decline and the subjects with SDAT showing progressive decline. The test showing the greatest decline over the four years was the logical memory subtest of the Wechsler Memory Scale, and the test showing the least decline was the Wechsler Memory Scale digit span forward subtest. Even the latter test, however, reflected much decline. There were five subjects with SDAT whose dementia remained mild throughout the four-year study. The others progressed to more severe levels. The five subjects performed more ably on each of the 16 tests than those who progressed to more severe levels. In fact, after an initial level of decline, several of the tests showed little or no decline among the five subjects. Four hypotheses are offered in examining the differences between those subjects whose dementia remained mild and those whose dementia did not.