We examined changes in avoidant and dependent personality disorder dimensions, and pre-treatment and in-treatment factors associated with such changes in 77 patients, randomized to medication-free residential cognitive (CT) or residential interpersonal therapy for social phobia. Personality disorders and personality dimensions according to the Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition (DSM-IV) were assessed at pre-treatment and at one-year post-treatment. Both treatments were associated with a decrease in avoidant and dependent personality dimensions; dependent dimension decreased more in CT. Changes in cognitive factors predicted changes in both personality dimensions, whereas changes in symptoms or interpersonal factors did not. Change in the cognitive factor estimated cost was the most powerful predictor in the avoidant dimension, as it was the only predictor that remained significant in the forward regression analyses. Change in the cognitive factor estimated cost, and treatment were the most powerful predictors of change in the dependent dimension. Pre-treatment use of anxiolytics predicted larger changes in both PD dimensions.