AbstractBackgroundThe EARLYSTIM trial demonstrated for Parkinson's disease patients with early motor complications that deep brain stimulation of the subthalamic nucleus (STN‐DBS) and best medical treatment (BMT) was superior to BMT alone.ObjectiveThis prospective, ancillary study on EARLYSTIM compared changes in blinded speech intelligibility assessment between STN‐DBS and BMT over 2 years, and secondary outcomes included non‐speech oral movements (maximum phonation time [MPT], oral diadochokinesis), physician‐ and patient‐reported assessments.MethodsSTN‐DBS (n = 102) and BMT (n = 99) groups underwent assessments on/off medication at baseline and 24 months (in four conditions: on/off medication, ON/OFF stimulation—for STN‐DBS). Words and sentences were randomly presented to blinded listeners, and speech intelligibility rate was measured. Statistical analyses compared changes between the STN‐DBS and BMT groups from baseline to 24 months.ResultsOver the 2‐year period, changes in speech intelligibility and MPT, as well as patient‐reported outcomes, were not different between groups, either off or on medication or OFF or ON stimulation, but most outcomes showed a nonsignificant trend toward worsening in both groups. Change in oral diadochokinesis was significantly different between STN‐DBS and BMT groups, on medication and OFF STN‐DBS, with patients in the STN‐DBS group performing slightly worse than patients under BMT only. A signal for clinical worsening with STN‐DBS was found for the individual speech item of the Unified Parkinson's Disease Rating Scale, Part III.ConclusionAt this early stage of the patients' disease, STN‐DBS did not result in a consistent deterioration in blinded speech intelligibility assessment and patient‐reported communication, as observed in studies of advanced Parkinson's Disease. © 2022 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.