Objective: It is commonly believed that some features of borderline personality disorder (BPD) improve as individuals reach their late 30s and 40s. This study examined age-related change in borderline criteria and functional impairment, testing the hypothesis that older age would be associated with relatively more improvement than younger age.

Method: A total of 216 male and female participants with BPD were followed prospectively with yearly assessments over 6 years.

Results: Participants showed similar rates of improvement in borderline features regardless of age. A significant age by study year interaction showed functioning in older subjects to reverse direction and begin to decline in the latter part of the follow-up, in contrast to younger subjects who maintained or continued improvement over the 6 years. Despite the decline, functioning for the older subjects was comparable with or slightly better at year 6 than at year 1.

Conclusion: Improvement in borderline features is not specific to the late 30s and 40s. There may be a reversal of improvement in functioning in some borderline patients in this older-age range.