Behavioral observations were conducted on aged mentally impaired females in an institutional environment on a weekly basis for a 2-year period. An eight-category taxonomy was used to rate the complexity level of the subjects' behaviors. Although the average weekly performance showed significant linear decline over the 2 years, half the subjects remained stable in the level of their behavioral functioning. In comparison to subjects exhibiting declines in level of functioning, the stable subjects evidenced less serious medical conditions, had better comprehension of their situations, were more socially reactive, manifested fewer neurotic conditions, and had greater control over impulses and aggression at the beginning of the project.