Elwood P. Dowd insists on including his friend Harvey in all of his sister Veta's social gatherings. The trouble is Harvey is an imaginary six-and-a-half-foot-tall rabbit. To avoid embarrassment for her family, and especially for her daughter Myrtle Mae, Veta decides Elwood should be committed. However, when a frantic Veta explains that years of living with Elwood's hallucination have caused her to see Harvey too, the doctors mistakenly commit her instead of her brother. When the truth comes out, it seems that Elwood and his invisible companion have had a strange influence on everyone, and in the end, even Veta realizes that maybe Harvey isn't so bad after all.