Up The Sandbox is a complex and difficult film, and it is ambiguous on many points, particularly on whether the protagonist Margaret Reynolds (Barbara Streisand) is a women's liberationist, a closet lesbian, or a masochist. Based on the novel by Anne Richardson Rolphe, it follows Margaret's attempts to tell her husband that she is pregnant with yet another child. The everyday events of her life are punctuated by numerous and complex fantasy sequences which reveal her fears and her desires. It is clear that she is afraid that she and her husband Paul (David Selby) are growing apart -- and that he may be having an affair. Despite the increasingly elaborate and frantic nature of her fantasies, her disclosure, when she finally makes it, has happy results.
~ Clarke Fountain, All Movie Guide