This study analyzes the variation in one measure of son preference that is of particular relevance in rural China: whether a woman considers it important to have a son, and the reasons why sons are important. To summarize our conclusions, we find that the expectation that a son will provide financial support in old age is strongly associated with the response that a son is important. This expectation is stronger in low income and mountainous villages, but it is weaker among women who earn cash income. The importance of a son is positively associated with ancestor worship and negatively associated with respondents' education, personal autonomy, the extent to which the husband shares housework, and exposure to the world beyond the village. We also find that sex-specific rates of infant mortality vary systematically with mother's response on the importance of a son, providing a test of the validity of our preference measure. (Contains 4 tables and 2 footnotes.)