A purported global decline in sperm counts has been a source of controversy since the early 1990s. Numerous studies performed since then, as well as reanalysis of the original data, show either no changes, or even increases, in sperm concentrations over time. In this review, we discuss the 1992 meta-analysis that initiated the continuing debate on whether sperm concentrations are declining, and the community discussion surrounding it over the past two decades. We also highlight studies evaluating sperm concentrations performed since the initial study that produced different results, and conclude that no definitive cause for a decrease in sperm counts has been established, and the effects of geography and environment on sperm counts are unclear.Approximately 15% of couples are considered infertile, with a male factor implicated in up to 50% of cases, underscoring the essential contribution of the male in conception. 1 However, only over the past two decades have we begun to understand the degree to which men contribute to a couple's infertility, which historically was attributed to the female partner. One quarter or more of infertile men have an unknown cause for their infertility, and while recent work suggests that many of these etiologies are genetic, we cannot exclude the impact of environmental factors on the male reproductive system, which have been incompletely defined.Work over recent decades has identified a potential decline in sperm concentrations, with at least one explanation being an increase or change in environmental pollutant levels. In 1992, a meta-analysis of sperm concentrations derived from 61 papers dating between 1938 and 1990 involving semen quality from 14 476 men found that both sperm concentrations and seminal volumes had dropped significantly during that period. 2 This was followed in 1993 by a manuscript suggesting that this decrease in sperm concentrations was partly due to environmental contamination with estrogenic compounds. However, there was little evidence identifying estrogens in the geographical areas where sperm concentrations appeared to be declining, or other evidence directly linking estrogenic pollution with declines in male fertility. 3 These works triggered a continuing discourse and numerous investigations to evaluate the verity of these claims. However, current data have failed to demonstrate a decrease in either sperm concentrations or male fertility.Owing to the large amount of unclear and confounding data, it is difficult to determine whether male fertility rates are truly declining. Fertility assessment in both men and women is made more difficult by the wide range of sperm concentrations that can result in pregnancy. Indeed, sperm count alone cannot define the fertility potential of a couple. Nevertheless, from the authors' viewpoint, the available data do not support a global decline in sperm concentrations or male fertility. We highlight the limitations of the original work claiming this decline, and show that current data, including data by the authors of the...