Vietnam recently demonstrated a skewed sex ratio at birth. Little research has examined postnatal impacts of son preference in Vietnam, such as in child health care seeking. Past research in other Asian countries with son preference has found that parents are more likely to take sons to a health facility when they are sick, to do so more promptly, and invest more resources in care, than daughters. Using data from a paediatric hospital emergency department, we analyse gender differences in illnesses, referral patterns, and outcomes among children to understand how gender disparities in paediatric hospital admissions arise. Almost twice as many boys were brought into the facility as girls. Compared to girls, boys were significantly more likely to have bypassed lower-level facilities and entered care at the tertiary facility, controlling for severity of illness and socio-demographic characteristics. This suggests parents provide preferential treatment to boys, potentially leading to excess morbidity among girls who become ill. However, we find no significant differences in delay of care seeking or evidence of provider bias. Ensuring that girls are able to access appropriate, quality care when needed, will improve equity of access to care for all children.