Police in Conroe say he has been reported missing once before, and was found in another state.
Thomas Conway Miller, 71, suffers from Alzheimer's and dementia. He was last seen wearing blue jeans and a long sleeved shirt.
Police believe he may be driving a blue 2000 Toyota Sienna van with Texas license plate 118 YTC. Anyone with information is asked to call Conroe police at 936-522-3200.