The aim of this paper is to analyze the determinants of public health expenditure in developing countries. This is done through an econometric analysis of panel data for 61 countries. A special interest is devoted to the role of external financial constraints, on corruption and on two aspects of the socio-politic situation : socio-politic unrest and ethnic structure. By highlighting the positive role of net transfers and external grants in the highly indebted poor countries, our results back the approach according to which the alleviation of debt burden in these countries could lead to an increase in public health expenditure, but we find no evidence of this potential effect for the other countries. Our results also bring to the fore the importance of corruption issues with the presence of a threshold above which corruption has a negative effect on public health expenditure. Socio-politic unrest have also a negative impact on public resources allocated to health. Ethnic dominance appears to free a room for maneuver the governments can use to increase public expenditures in health sector. Our results also emphasizes the absence of any statistic relation between the populations' health status as a determinant of public health expenditure.