Theory predicts that patients completing psychoanalysis should improve in their dynamic functioning. The aim of this naturalistic study is to examine whether a sample of 17 subjects from the Penn Psychoanalytic Treatment Collection with completed, tape-recorded psychoanalyses demonstrated improvement in one dynamic aspect: their defense mechanisms. The pre-post effect size for the change in overall defensive functioning (ODF) of the sample was large (.76) and statistically significant (p = .01). The percentage of subjects who improved in their ODF (71%) was similar to that found by others who studied the same sample using general functioning measures. These findings provide the first empirical evidence to support a trait-like change in dynamic personality functioning in patients who have undergone psychoanalysis. Randomized controlled studies with homogeneous samples are needed to further confirm these findings.