The 51-year-old woman detained on suspicion of killing the four people is an employee at the clinic.
Officers called to the Oberlin Clinic shortly before 9pm on Wednesday and found the victims and a fifth person who was seriously injured in patient rooms, Brandenburg state police said.
“The victims showed signs of significant external violence,” police spokesman Thorsten Herbst said.
Police were still investigating the exact circumstances but said the detained woman was “urgently suspected” of the killings.
Local newspaper Potsdamer Neueste Nachrichten reported the victims were residents of the Thusnelda von Saldern House, which cares for people with serious disabilities.
Potsdam is on the southwestern edge of the German capital, Berlin.
SOURCE: The Associated Press