For metabolic syndrome and diabetes, interpretation of published data is difficult due to a number of issues including ambiguities in information reported on study design, non-comparable shift work patterns, emphasis on non-significant increases in risks or highlighting of positive results from subgroup analyses, insufficient or unclear model adjustments andthe absence of a widely accepted definition for metabolic syndrome. For metabolic syndrome, on the basis of mostly statistically significantly positive findings but these methodological limitations, we grade the epidemiological evidence as moderate (RCGP **). For diabetes, based on the fact that there were several studies but only one study reported a statistically significantly elevated risk among shift workers and the issues discussed above, we grade the epidemiological evidence as limited (RCGP *).