OBJECTIVES: Season of birth has been associated with adult morbidity and mortality, but few epidemiological studies have examined whether season of birth contributes to the development of cancer. Using data from the Australian National Endometrial Cancer Study, a population-based case-control study of 1399 cases and 1539 controls, we examined the association between season of birth and risk of endometrial cancer. METHODS: Unconditional logistic regression was used to estimate odds ratios (OR) and 95% confidence intervals (95% CI) for the association between season of birth and endometrial cancer. Additional analyses were stratified by state of birth. RESULTS: Season of birth was not associated with endometrial cancer overall, but there was an increased risk among women born in summer in Tasmania, the most southerly state (OR = 4.46, 95% CI: 1.24-16.06) and non-significant increases in the other southern states. CONCLUSION: Further data are required to confirm these findings, however the observed associations may be due to the longer days and/or greater hours of sunshine in Australia's southerly states in summer, suppressing melatonin levels in summer-born infants and predisposing them to cancer in adulthood.; Ingrid J Rowlands, Philip Weinstein...