In order to discover the prevalence of signs and symptoms of temporomandibular disorders (TMD) in Japan, and the difference in the prevalence among various sex and age groups in the Japanese population, 672 individuals (304 males and 368 females, age range 20-92 years) were selected randomly in Okayama City, Japan, and were investigated by means of questionnaires and clinical examinations. The reported frequency of symptoms was: TMJ sounds 24%, facial-TMJ-jaw pain 11%, headache 27%, teeth clenching 30%, and grinding 34%. The percent frequency of the following signs was: impaired mouth opening 5%, clicking 46%, reciprocal clicking 20%, crepitus 19%, TMJ tenderness 6%, and masticatory muscle tenderness 21%. The subjects with TMJ clicking were more frequently females than males. TMD signs and symptoms were found to be common in all age groups, but they were fewer in the older than in the younger age group. The younger-aged subjects with clicking appeared with significant frequency, whereas crepitus was populated with significant frequency by the oldest age group.