The author analyzes trends of declining maternal-age-specific dizygotic twinning rates in Europe for the period 1960-80. Using data from country publications on vital statistics, rates were available for most European countries; no useful data was, however, available for Albania, Romania, and Turkey. Dizygotic twinning rates declined for most countries tries through the 1970s, yet ceased their decline in the 1970s following initial drops in the 1960s were England and Wales, Scotland, Sweden, Norway, Denmark, Switzerland, Hungary, and Czechoslovakia. In the absence of concrete reasons for the observed twinning rates declines and subsequent decline cessation in several countries, the author hypothesizes potential causes. It is speculated that declining sperm quality over the period is related to the declines in European dizygotic twinning rates. Specifically, environmental pollution may have been at the root of deteriorating sperm quality, which in turn fueled the observed declines in dizygotic twinning rates. Cessation of the rate declines for selected countries in the 1970s may be related to the removal of certain polluting environmental agents from those countries. Forming 2 geographic European subregions, countries experiencing rate decline cessation or increase may have common elements to their environmental policy which foster the improvement of sperm quality. Examination of regulations regarding certain agents in these countries within a few years of 1970 may help identify agents responsible for dizygotic twinning rate trends in most European countries. The author also suggests that rate decline cessation may have stemmed from an increase in hormonally-induced twinning, counterbalancing the decline in natural twinning over the period.