The prevalence rate of hyperostosis, defined as the presence of complete bony bridges linking two vertebrae in at least two separate sites in the dorsal spine, was studied in a sample of some 9 000 persons who were 40 years of age or older and were representative of the general population of Finland. The standardized rates of hyperostosis were 3.8% for men and 2.6% for women. The prevalence rates rose sharply with age, and depending on the age group, the male-female ratio varied between 1.4 and 2.1. The adjusted rate of hyperostosis was higher in East Finland than elsewhere. There was a suggestion of hyperostosis being associated with a higher mortality rate as judged by regional variations and by analysis of matched case-controled pairs. There was no evidence that locomotor symptoms occurred in excess in subjects with hyperostosis; nor was prior traumatic experience more common.