Objective assessment of clinical findings of patients with Huntington's disease (HD) is necessary for an evaluation of the individual progression of the disease and the effect of therapy, and it requires specific assessment scales. The Unified Huntington's Disease Rating Scale (UHDRS) is an overall scale to assess clinical performance and functional capacity. In the course of carrying out studies in HD, several items in the motor function section were found to be difficult to score, had high cognitive loading, and appeared to be redundant. The objective of this study was to shorten the motor section of the UHDRS to the smallest number of items, without loss of internal consistency, while still assessing the important clinical features of HD. Shortening the total motor score of the UHDRS was carried out on the UHDRS data set of the Leiden University Hospital using four methods. The first two methods employed principal-component analysis with Varimax rotation. Strongly interrelated test items were uncovered, resulting in a reduction of test items to a smaller set. The third method reduced items so that the internal consistency (Cronbach's alpha) was maximal. The fourth method omitted items subjectively. The results of the Dutch data set were validated on follow-up data and on a data set from the University of Rochester Medical Center, New York. This study determined that the number of items in the motor function section could be reduced from 31 to 15. The reduced set maintains the relationships between the motor and other sections of the UHDRS and still assesses the major clinical features of HD.