Background: Typical hypomimia develops in almost all Parkinson's disease (PD) patients. We observed the presence of hemihypomimia (HH) in some of our PD patients. Objective: To discern the presence of hemihypomimia, to compare clinical features of these patients with the patients without HH and then to evaluate HH prospectively. Methods: Among 353 patients with PD followed-up between September 2003 and December 2004, 204 patients in stage 2 of Hoehn-Yahr were evaluated and hemihypomimia was observed in 13 PD patients (6.4%). Two groups were compared with respect to the age of onset of the first PD symptom, duration of PD and the body side affected predominantly. In addition, persistence of HH was prospectively evaluated in 11 of 13 patients with HH up to two-year-follow up period. Results: Hemihypomimia was interestingly on the right side of the face in all patients. Of these 13 HH patients, all but one had predominantly right-sided PD symptomatology. In the comparison of HH patients with the remaining group (n = 191), patients with HH had significantly earlier onset of PD symptoms (mean: 53.9 vs 58.5 years), and shorter PD duration (mean: 4.0 vs 6.2 years) (p < 0.01). Up to two-year-follow up, hemihypomimia, which was not changed by several triggered emotional facial expressions, clinically persisted. Conclusion: Our observations suggest that hemihypomimia is a rare phenomenon in PD, especially in PD patients having early-onset and shorter PD duration which may persist for several years in concordance with typical asymmetrical involvement of the limbs. HH developed in the right side, prominently on the lower part of the face. Understanding the underlying mechanism(s) about how hemihypomimia appears, and why it dominantly affects the right side of the face deserves further assessment.