OBJECTIVES:   To assess sensitivity of the EQ-5D to clinical change in patients with Parkinson’s disease with moderate to severe L-dopa induced dyskinesias. METHODS:   Using data from a Phase IIB, randomized, 13-week, double-blind, placebo-controlled, dose-response study of AFQ056, a mGluR5 antagonist, we identified all patients with non-missing values for the modified Abnormal Involuntary Movement Scale (mAIMS) and the EQ-5D at baseline and week-9 administrations.  Patients were pooled across all six treatment groups (5 active drug, 1 placebo).  Concurrent validity and responsiveness to clinical change were examined for the EQ-5D utility index (range -0.59 - 1.0, with 1 representing perfect health), visual analog scale (VAS) (range 0 - 100, with 100 representing perfect health), and individual item scores (ranging from no problems to major problems [3]), using the mAIMS (range 0 - 24, with 24 representing severe dyskinesias) as the criterion variable. RESULTS:   Among 197 randomized subjects, 149 (75.6%) had non-missing values for the EQ-5D and the mAIMS at baseline and week 9.  The mean (SD) mAIMS total score at baseline was 13.5 (4.8); this measure was uncorrelated with all EQ-5D item responses.  At week 9, however, mAIMS scores were generally higher for patients who reported more problems on EQ-5D item responses.  While mAIMS scores improved by an average of 4.8 points between the baseline and week-9 assessments, the mean EQ-5D utility score and EQ-5D VAS improved by only 0.024 and 0.05, respectively, and the number with better EQ-5D item responses was approximately equal to the number with worse responses. CONCLUSIONS:   The EQ-5D demonstrated limited concurrent validity in Parkinson’s disease patients with moderate to severe L-dopa induced dyskinesias, and the EQ-5D utility index and VAS were unresponsive to clinical change.  Evidence to support use of the EQ-5D in this population remains inadequate.