S&P Global Ratings' long-term rating on Massachusetts Development Finance Agency's series 2014P-1 tax-exempt bonds issued for Children?s Hospital of Boston (Children's) is 'AA'. Our rating on Children's series 2017A taxable bonds is also 'AA'. The outlook is stable. The rating reflects Children's exceptional balance-sheet metrics with extraordinary unrestricted reserves and light debt, coupled with a robust enterprise profile reflecting its clinical strengths, market position, and lower-than-expected reliance on Medicaid compared with other pediatric hospitals. Children's support of research and certain clinical programs dampens strong performance at the hospital, but management considers this support critical to its mission, goals, and recruitment efforts. We believe Children's balance-sheet strengths and philanthropic support are sufficient to offset any concerns about relatively thin debt service