Assessment of the functional status in patients with blepharospasm is of major importance for clinical practice and outcome studies. The Blepharospasm Disability Scale (BDS) is specifically directed to measure the disability in these patients. The metric properties of this instrument were evaluated. Reliability, validity, and responsiveness to within-patient health changes over time of the BDS were assessed in 40 patients with essential blepharospasm treated with botulinum toxin injections. The reliability of the scale was sufficient for use on group level (Cronbach's α coefficient, 0.69). Evidence of discriminant validity was provided by the difference in median score on the BDS between 21 newly admitted patients and 19 patients already under treatment (p < 0.001). Convergent validity was supported by correlations between BDS and neurological impairment scores (range, Spearman correlation coefficients, 0.65-0.79). Responsiveness to health changes was demonstrated by a significant difference between median BDS scores before treatment and 2 weeks after treatment with botulinum toxin (p < 0.01). The BDS is a useful disease-specific instrument to assess disability. Completion of the questionnaire is easy and takes only a few minutes. The instrument is suitable for use in patient care, descriptive outcome studies, and should be considered in controlled clinical trials.