Emerging evidence suggests that the peripheral immune system has an active role in the progression of Parkinson's disease (PD). The finding of T‑helper (Th; CD4+) cells infiltrating into the substantia nigra in PD patients demonstrated that Th cells are involved in PD. However, the association between peripheral T‑helper cell sub‑sets (Th1, Th2, Treg and Th17) and the sub‑set balance (Th1/Th2 and Th17/Treg) and PD has remained elusive. In the present study, sixty PD patients of the First Affiliated Hospital of Bengbu Medical College as well as 40 age‑ and environment‑matched healthy individuals were enrolled. The fraction of CD4+ T cells in the peripheral blood was assessed by automated hematology analysis and its sub‑sets (Thl, Th2, Thl7, Treg) were quantified by flow cytometry. The results showed that in the PD group, the proportion of Th1 and Th17 cells was increased, while that of Th2 and Treg cells was decreased. Compared with the control group, the Th1/Th2 and Th17/Treg ratios were significantly enhanced, and shifted towards Th1 and Th17, respectively. Furthermore, this Th1‑type response (Th1/Th2 balance shifting towards Th1) were associated with motor function scores determined by Unified Parkinson's Disease Rating Scale III (UPDRS‑III) scores. However, no correlation was found between the change in the Th17/Treg cell balance (Th17/Treg balance shifting towards Th1) and UPDRS‑III scores. These data supported that chronic immune stimulation, specifically CD4+‑cell sub‑set imbalance, is linked to PD pathobiology and disease severity. CD4+‑cell sub‑sets and their imbalance may therefore represent novel biomarkers or therapeutic targets for PD.