National statistics for England and Wales for the period of 1950-79 were examined to study the secular trends in multiple myeloma mortality and to evaluate the extent to which these changes may be due to biases associated with improvements in medical care. Age-adjusted mortality has increased more than fivefold during this 30-year period. Contrary to the impression obtained from clinical series, a slightly greater increase in age-adjusted mortality has occurred in males. Examination of age- and sex-specific mortality trends showed that the greatest apparent increase in myeloma mortality occurred in individuals over 70 years of age. The data are consistent with either a cohort effect, indicating a true increase in mortality, or an age-dependent diagnostic effect in which a greater percentage of deaths among the elderly are now being certified as myeloma. Analyses of mortality data by social class and region point toward improved case ascertainment being responsible for at least part of the apparent increase in reported mortality. The increase in reported mortality in the younger age groups may reflect a true increase in the incidence of this disease. This increase, however, would account for only a proportion of the total increase, even when extrapolated to the older age groups.