This study evaluated poor mood state as a moderator of changes in verbal recall ability from before to after unilateral posteroventral pallidotomy in 54 individuals with advanced Parkinson's disease. Repeated-measures analysis of covariance (controlling for motor disease severity) indicated that left-posteroventral pallidotomy subjects with depressed mood performed more poorly on measures of verbal list learning and story recall compared to nondepressed subjects or right-posteroventral pallidotomy subjects with depressed mood both before and after surgery. The results suggest that depressed mood should be taken into account when interpreting memory test performance in Parkinson's disease surgical candidates both before and after surgery.