[1] He worked for twelve years at Haynes Memorial Hospital in Boston, where he treated thousands of patients with various infectious diseases.
In 1957, he transferred to Tufts Medical Center as chief of infectious diseases for adult medicine and pediatrics, and remained there until moving to Brigham and Women's Hospital in 1975.
[1][4] Fellow Boston infectious diseases physician Morton N. Swartz described Weinstein as "a bridge between the eras before and after the introduction of antibiotics".
[1] He played a significant role in the New England polio epidemics of 1949 and 1955; when obstetricians refused to see polio-infected pregnant women because they feared viral transmission, Weinstein delivered the babies.
He traveled across New England to make house calls, and on one occasion was summoned to Paris to treat Aristotle Onassis for pneumonia.