Decrease of olfactory function in patients with Parkinson's disease (PD) is a well-investigated fact. The present study aimed to investigate olfaction in PD patients with a specific focus on the effects of deep brain stimulation in the subthalamic nucleus. Eleven patients (age 42-67 years) participated in this study. Using the "Sniffin' Sticks", olfactory function was assessed based on butanol odor thresholds and the patients' ability to discriminate odors. Measures were taken with the stimulator being switched ON and OFF, respectively. While deep brain stimulation had no effect on odor thresholds, in hyposmic PD patients odor discrimination was found to be significantly higher during the ON period. This may indicate that deep brain stimulation has a positive effect on the cognitive processing of olfactory information in PD patients.