Adler served in the United States Army from 1966 through 1968. He continued his career thereafter, firmly straddling the two worlds of Yiddish and American Theatre. After much success in regional theatre, Adler made his Broadway debut as Ali Hakim, the Peddler, in the 35th anniversary production of Oklahoma! in 1979. He was following in the footsteps of actor Joseph Buloff, who had created the role in 1943, and also had a huge background on the Yiddish stage. Other Broadway shows included Oh, Brother! (1981), Sunday in the Park with George (1984 & 1994), Broadway (1987), Rumors (1988), Those Were The Days (1991), where he won the Drama Desk Award, and Crazy for You (1992). Adler stayed with Crazy for You for the entirety of its four-year run on Broadway.
Off-Broadway, Adler appeared in several well-received Yiddish speaking and Jewish-themed productions of the last 30 years, including The Golden Land (1985), On Second Avenue (1987),The Rise of David Levinsky (1987) and many others. He appeared in many summer productions at The Muny Theater in St. Louis. He had a voice role in Disney's animated film, Beauty and the Beast, Peddler in Disney's Aladdin, as well as roles in television shows such as Law & Order.