In October of 2007, an IARC panel of 24 scientists systematically evaluated epidemiologic, experimental, and mechanistic data and concluded that shift work that involves circadian or chronodisruption is probably carcinogenic in humans. In view of the possible scope of the problem—shift work is widespread and unavoidable on one hand and breast cancer and prostate cancer, which may be causally associated with chronodisruption, are epidemic worldwide on the other—German representatives of science and occupational medicine discussed the experimental and epidemiologic background and possible implications of the challenge identified by the International Agency for Research on Cancer (IARC) at a colloquium in Cologne in September 2008. This overview summarizes the key ideas presented at the Cologne Colloquium and offers 10 theses concerning the need for targeted studies and the necessity to develop possible means of prevention.