Lisa Gerritsen was born Leisa Orszag, and is the granddaughter of child actor and Screenwriter True Eames Boardman, and the great-granddaughter of silent film actors True Boardman and Virginia True Boardman. Her acting career began when she was eight years old. Encouraged by her mother and grandfather, and after running the gamut of numerous casting calls, she landed her first professional role in an episode of The Doris Day Show in 1968. After The Doris Day Show, Gerritsen had guest-star or cameo appearances in several television shows including The Odd Couple, Bonanza, The Courtship of Eddie's Father, The Virginian and Family Affair.
She was also cast in several episodes of Gunsmoke, one of which helped her to land a regular role in the 1969 NBC comedy series My World and Welcome to It, which starred william Windom and Joan Hotchkis. The show was based on the cartoons and comedy of author James Thurber.
In 1970, she was cast as Bess Lindstrom, daughter of landlord Phyllis Lindstrom (Cloris Leachman) in The Mary Tyler Moore Show, for which she received critical acclaim. Bess was a precocious child whose mother believed in progressive parenting—Bess always called Phyllis by her first name, read Phyllis' books on child rearing, and was educated on sexuality.
As Phyllis's daughter, Lisa Gerritsen established her importance to The Mary Tyler Moore Show in its very first episode. Though she returned only sporadically for the next few years, she was memorable playing an off-beat, brainy, talented little girl. In the premiere episode, test audiences didn't like Rhoda, played by Valerie Harper. Harper eventually became one of the most popular stars on TV, but her initial change from antagonist of Mary (which the audience disliked, since Mary Tyler Moore was universally loved by viewers) occurred because of Bess (Gerritsen). Because Bess likes Rhoda and thinks she's funny, to the eternal consternation of Phyllis, the audience changed their opinion of her too, and by the second episode she was Mary's best friend. Gerritsen returned in the role in the spin-off series Phyllis (1975–1977).
