An index, called the mucosal-plaque score (MPS), was tested for intra- and inter-examiner agreement at an institution for elderly individuals with mental disabilities. This index was designed to evaluate oral health and oral hygiene in groups of individuals, particularly in hospitals or at other institutions. MPS consists of the sum of a four-point mucosal score (MS) and a four-point plaque score (PS). Intra-examiner agreement was assessed for one dentist (BMH), who examined 24 individuals twice with a one-week interval. Weighted kappa values were 0.60 for MS, 0.62 for PS, and 0.62 for MPS. Inter-examiner agreement between two dentists was conducted by duplicate examinations on 20 persons. Weighted kappa values were 0.47 for MS, 0.71 for PS, and 0.70 for MPS. In a second assessment of Inter-examiner-agreement, eight individuals were each examined by a dentist, two dental hygienists, and one medical nurse. Weighted kappa values were 0.79 for MS, 0.80 for PS, and 0.77 for MPS. These results support the conclusion that the MPS can serve as a reliable measure for the assessment of oral health care in groups of older Individuals.