After returning to Puerto Rico in 1859, Betances established a very successful surgery and ophthalmology practice in Mayagüez. Even fierce political enemies such as Spanish pro-monarchy journalist José Pérez Morís regarded Betances as the best surgeon in Puerto Rico at the time. His good reputation in Puerto Rico would survive his stay in the island nation for many years. In 1895, while Betances was living in Paris, the manufacturers of the "Emulsión de Scott" (a codfish liver oil product that is still sold today, manufactured by GlaxoSmithKline in modern times), paid an endorsement fee to Betances to have him appear on advertisements on Spanish language magazines and newspapers all over New York City and the Caribbean, based on his solid reputation as a doctor.