The purpose of this study was to establish criteria for the visual evaluation of oral hygiene by analyzing the relationship between status of oral hygiene and number of oral bacteria in saliva for use in predicting the development of pneumonia. A total of 145 Japanese people of advanced age living in nursing homes were enrolled in the study. We evaluated the Dental Plaque Index (DPI) and Tongue Plaque Index (TPI) as simple measures of status of oral hygiene. We also determined the number of viable microorganisms in the saliva of each subject. The relationship between the status of oral hygiene and episodes of pneumonia was investigated over a period of one year. Dentate patients with poor oral hygiene as indicated by their DPI and TPI scores demonstrated significantly higher salivary bacterial counts than those with a good score for oral hygiene (p<0.01 and p<0.05, respectively). Both the number of febrile days was significantly higher (p=0.0012), and number of patients developing pneumonia larger (p<0.01) in dentate patients with DPI-based poor scores than those with DPI-based good scores. These results demonstrate a significant positive correlation between salivary bacteria and visual evaluation of oral hygiene in dentate patients according to number of febrile days and development of pneumonia.