Objective: To estimate underreporting of fetus and infant deaths having congenital syphilis as their underlying or associated cause in Recife, Pernambuco, Brazil, between 2010-2016. Methods: Probabilistic database linkage was carried out between congenital syphilis cases recorded on the Notifiable Health Conditions Information System and fetus and infant deaths due to congenital syphilis recorded on the Mortality Information System. Results: 170 fetus and infant congenital syphilis deaths were matched. Fetus and infant deaths due to congenital syphilis were underreported by 80.9% on the Notifiable Health Conditions Information System and by 7.0% on the Mortality Information System, accounting for an increase of 2.3% and 7.0% in the final databases, respectively. Conclusion: The underreporting identified compromises knowledge of the true magnitude of deaths caused by this disease.