The purpose of this paper is to describe the effect of 5 years of subthalamic nucleus deep brain stimulation (STN DBS) on levodopa-induced complications, both in everyday life and during an acute challenge with levodopa. Thirty three patients were evaluated during an acute levodopa challenge before surgery and then 1 and 5 years afterwards (both off stim and on stim), using the UPDRS III scale and the CAPSIT-PD scales for dystonia and peak-dose dyskinesia. The UPDRS IV scale was used to assess motor complications in everyday life. The levodopa daily dose and DBS parameters were also recorded. Levodopa-induced complications in everyday life (UPDRS IV) and during an acute levodopa challenge had improved markedly after 1 year (both on and off stim) and still further at 5 years. Peak-dose dyskinesia decreased between the 1- and 5-year measurements. STN DBS decreases levodopa-induced motor complications over the long term. This phenomenon may be explained by (a) overall stabilization of the basal ganglia network and (b) striatal synaptic changes. Our results suggest that DBS leads to both qualitative and quantitative modulations in the corticostriatal loops.