This research aims to further current understanding of gender differences in old age mortality. In particular, it assesses the relative importance of health behavior and baseline health conditions in predicting the risk of dying, and how their effects differ between elderly men and women. Data for this research came from a prospective study of a national sample of 2,200 older adults in Japan from 1987 to 1999. Hazard rate models were employed to ascertain the interaction effects involving gender and health behavior (i.e., smoking and drinking) and baseline health status. Gender differences in old age mortality in the Japanese are quite pronounced throughout all of our models. In addition, interaction effects of gender and smoking, functional limitation, and cognitive impairment, indicate that females in Japan suffer more from these risk factors than do their male counterparts. Failure to adjust for population heterogeneity may lead to a significant underestimation of female advantage in survival. The inclusion of health behavior and health status measures only offsets a limited proportion of this gender differential. The increased mortality risk due to smoking, functional limitation, and cognitive impairment among elderly Japanese women suggests that narrowing of gender gap in mortality may be due to not only changes in the levels of these risk factors but also their differential effects on men and women.