The arrests are related to an investigation by the Puerto Rico legislature into allegations that the licencing board altered the results of low-scoring tests and awarded licences to candidates who did not qualify.
Members of the board took bribes of as much as $6,000 to change the grades of failing exams, Rosa Emilia Rodriguez, interim US attorney, said.
Pablo Valentin, a former executive director of the medical licencing board, was among those arrested by Food and Drug Administration agents and local police.
Most of the suspects are Puerto Ricans who studied in the Dominican Republic, Mexico or Cuba before taking an exam to allow them to practice medicine in the Caribbean territory, she added.
The defendants will face charges including mail fraud and making false statements to Medicare, the US government administered healthcare insurance system.
"We cannot allow doctors who obtained their licence in an irregular way to practice medicine," Rosa Perez Perdomo, Puerto Rico's health department secretary, said in a written statement.
"The health of Puerto Ricans has to be protected at all costs."