Objectives This study was conducted to examine modification in heat-related mortality in the Netherlands by sociodemographic and geographical factors including socioeconomic position and population density (PD).Design This observational study applied time series analysis on daily mortality counts according to mean daily temperature (°C).Setting Statistics Netherlands.Participants Death registrations in 2006, 2018 and 2019 from residents registered at the Dutch Personal Records Database, restricted to deaths in the period between April and October.Main outcome measures Assuming a V-like relation between temperature and mortality, a segmented linear model was used to estimate the temperature effects on mortality. In order to estimate the effects of severe heat, a second model including a heat threshold of 22°C was included in the model. We stratified by sociodemographic groups, calendar year and the five main causes of death (cardiovascular, respiratory, neoplasm, psychological and nervous system, and other) and controlled for time trend and seasonality.Results The effect of 1°C increase in temperature whereby the mean daily temperature exceeded 16°C was a 1.57% (95% CI 1.51% to 1.63%) increase in mortality among the total population. In temperature segments whereby the mean daily temperature exceeded 22°C, this effect was 2.84% (95% CI 2.73% to 2.93%). Low-income groups were at higher risk of heat-related mortality, compared with high-income groups. Areas with a high PD show relatively weak effects within both the warm and heat segments.Conclusion Results of this study highlight the variation in terms of heat vulnerability among the Dutch population, whereby poor living conditions specifically may increase the effect on high temperature on mortality.