Preterm birth is a leading cause of death in children under 5 years in low and middle income countries, and a major determinant of neonatal mortality and morbidity globally. The aim of this study was to assess the total cost of preterm infant treatment, as well as the financial contribution made by families in provincial and national hospitals. Cross-sectional medical and financial data were collected in one purposely chosen provincial, as well as in one purposely chosen national hospital. Cost data for all infants discharged from the two hospitals in 2017 were collected and analyzed. Average total medical cost per child was USD 1,643.52 in the national hospital and USD 668.94 in the provincial hospital. Mean medical out-of-pocket expenditure was USD 60 at the national hospital. No medical out of pocket expenditure was reported at the provincial hospital when parents complied with national health insurance policies. Substantial financial penalties were found for bypassing lower level facilities. Parents seeking care at specialized hospitals without medical authorization paid on average an additional USD 240, which corresponds to 111% of the average monthly wage in Vietnam.