In Thailand, like the U.S., women's higher rates of illness and health service use imply that they are "sicker." But, as in the U.S., females live longer than males. Based on a large representative sample of Bangkokians, we find that married women report more sickness, are more likely to utilize health services and, according to self-reports, have poorer health. Western literature suggests five prominent explanations for gender differences in health: biological risks, acquired risks, psychosocial aspects of symptoms and care, health-reporting behavior, and prior health care and caretakers. However, analyses show that these explanations largely fail to account for morbidity differences between Thai men and women. The observed gender differences in health among Thais remain significant after eliminating pregnant women and new mothers, and after controlling for several aspects of acquired risk. Problems associated with the reproductive system among Thai women, along with greater psychological distress, appear to account for most of the gender differences in health. The theoretical implications of these findings are discussed. As for the apparent contradiction between gender differences in health and mortality in Thailand, the evidence indicates that Thai men, like their American counterparts, suffer from more serious chronic ailments that may explain their higher mortality rates.