Using regression analyses with a sample of over one million under 5 children across 66 developing nations from the Demographic and Health Survey, this study explores the impact of son preference on health disparities between male and female children. The authors consider the Grossman Theory (1972), which suggests health as a lasting "capital stock in the production of healthy time". The idea is that health gradually diminishes and can be restored through investments in various health-related factors such as nutrition and medical services. Although parents with son preference may make distinct and rational investments in both genders, favoritism may impact the health outcomes of female children. The authors suggest that the degree of son preference's impact will vary between families according to their socio-economic background. There is support for both hypotheses, since the results show that son preference enhances health disparities based on gender and disproportionately affects female children of lower socioeconomic backgrounds.