Deep brain stimulation (DBS) of the subthalamic nucleus (STN) has become an established therapeutic option for advanced Parkin- son’s disease (PD). In this study, the effects of unilateral and bilateral STN stimulation on spontaneous language production are explored, by comparing linguistic performance in different stim- ulation conditions with normative data of healthy subjects. Language samples of ten PD patients with DBS of the STN were obtained in four stimulation conditions: bilateral stimulation on, bilateral stimulation off, stimulation of the left STN only and stimulation of the right STN only. The spontaneous language production differed from the normative data in all four stimulation conditions. Especially morphosyntactic elements of spontaneous language production were altered. Despite these linguistic differences with normal controls no significant differences be- tween stimulation conditions were found. These results emphasize that the effects of STN stimulation on spontaneous language pro- duction reflect a complex interplay of multiple factors.