Background This study examined the nature of ecological associations between ‘religiousness’ and suicide rates (1985–1994) in the 11 provinces in the Netherlands. Methods indices of religiousness, obtained from a nationwide survey, were used as aggreg ate predictors of provincial suicide rates in weighted linear regressions, and as individual-level predictors of suicide acceptance in logistic regressions. Socio demographic confounding was controlled for. Results Orthodox beliefs and religious affiliation were the best predictors of lower suicide acceptance in individuals and of lower suicide rates in provinces. The ecological association was most pronounced in the least religious parts of the country givingrise to a curvilinear ecological regression line. Conclusions Curvilinear ecological regression lines arise when mean levels of exposure affect individual risk above and beyond personal exposure i.e. when there is ecological effect modification. This study demonstrates that such contextual effects, respons ible for cross-level bias, apply to the association between suicide and religious ness. Variation, from context to context, of the effects of exposure to psychosocial risk or protective factors for outcomes such as suicide, has important implications for research and prevention.