Ten Parkinson's Disease (PD) patients and 10 control participants were tested using a task-switching paradigm in which there was a random task sequence, and the task was cued in every trial. Five PD patients showed a unique error profile. Their performance approximated guessing when accuracy was dependent on correct task identification, and was nearly perfect when accuracy did not depend on correct task identification or in conditions without task switching. Nonetheless, PD patients showed normal task-rule implementation, evidenced by their preparation-related reduction in the reaction-time task-switching cost. The results indicate that, without redundant task information, some PD patients have a specific goal setting deficit, reflected in a difficulty determining which task is currently relevant.