She made her television debut in 1961 on Armstrong Circle Theatre in The Fortune Tellers, starring opposite Val Avery.
The following year, she moved to New York City, making her Off-Broadway debut as the title character in William Snyder's The Days and Nights of BeeBee Fenstermaker at the Sheridan Square Playhouse, a production which included Robert Duvall.
(1971), Ruth in Desperate Characters (1971), Angela in Mr. Ricco (1975), Elaine Cassel in Eyes of Laura Mars (1978) and Brenda Samuels in True Confessions (1981).
[3] In 1977, Gregorio returned to Broadway after an eight-year hiatus in the original production of Michael Cristofer's The Shadow Box as Agnes; she garnered nominations for the Tony Award for Best Performance by a Featured Actress in a Play and the Drama Desk Award for Outstanding Featured Actress in a Play.
In 1993, she appeared as Karen Frick in the Manhattan Theatre Club's production of Arthur Miller's The Last Yankee, and in 2000, she portrayed the roles of Lena and Sandra in Beth Henley's Family Week at the Century Center for the Performing Arts.
[4] In 1977, Gregorio received the Clarence Derwent and Drama Desk Awards, as well as a Tony nomination, for her portrayal of Agnes in the original production of Michael Cristofer's The Shadow Box.