Changes in death rates from malignant tumours of bone among successive cohorts in the U S A and in England and Wales are shown to be remarkably similar. Since cohorts born in the 1870's there have been simultaneous and equal declines in both countries and in both sexes. Comparable cohort trends are also shown for Paget's disease, although the death rates in the U S A are only about one-fifth of those in England and Wales.