Sallie Ann Cappello, 54, of Valley Forge Circle in King of Prussia, has been missing since Wednesday.
Police say Cappello left her home for "unknown reasons" and has not been heard from since.
Cappello suffers from various medical conditions and does not have her medication, police said.
Cappello is described as a white female, 5 feet 4 inches tall, medium build with shoulder length brown curly hair.
She may be wearing a gray hooded sweat jacket over a white shirt, gray jeans, sneakers, and carrying a black fanny pack.
Upper Merion Police ask that anyone with information on Cappello call them at 610-265-3232.