Solifenacin-induced cognitive adverse effects have not been reported frequently, but solifenacin-induced delirium and hallucinations with successful switching to darifenacin, without additional drug, have not been reported in the literature. In this case report, we present an 80-year-old Caucasian male with insomnia and anxiety symptoms and overactive bladder who developed delirium and hallucinations when treated with solifenacin and trazodone. After solifenacin discontinuation and switching to darifenacin, symptoms significantly improved immediately. Such a case has not yet been described in literature; however, an adverse effect associated with solifenacin can occur, as this report clearly demonstrates.