After moving to Los Angeles, Kidder was cast opposite Gene Wilder in "Quackser Fortune Has a Cousin in the Bronx" (1970) as an exchange student in Ireland who becomes the love interest of a poor horse manure collector in Dublin whom she almost runs over with her car. After filming in Ireland, Kidder relocated to New York City to further study acting. A year later, she returned to California, and was cast in the Brian De Palma film "Sisters" (1973), which gained notoriety for both director and Kidder, who as leading lady, portrayed conjoined twins, one of whom is a suspect in a brutal murder. Kidder had been in a relationship with De Palma at the time, and had been roommates with co-star Jennifer Salt in Los Angeles. "Sisters" went on to achieve critical recognition, being considered among the best American films of the decade by critic Robin Wood, as well as one of the most important films in Kidder's career by film critic G. Allen Johnson.