The variability of mean monthly temperatures in the United States since 1896 is examined. The results show that the interannual variability reached a peak in the decade centered on 1930 and decreased fairly steadily to a minimum in the decade centered on 1970. This temporal trend is almost completely explained by changes in the variability of winter (December, January, February) mean monthly temperatures. The greatest percent decrease in variability occurred in the Midwest. © 1979 D. Reidel Publishing Company.