Estanislao Roch, 81, lives on Lausanne Avenue in Daly City but has been known to walk to his daughter's house on Edinburgh Street in San Francisco, more than two miles away.
He went for a walk at about 9:45 a.m. Friday and did not return. Daly City police Lt. Jay Morena said today the family is gravely concerned about Roch, who requires daily medication.
Police have scoured a two-mile radius around his home, posted missing-person flyers and checked local hospitals, but have not found Roch.
"We've posted these flyers at just about every business in Daly City and along the San Francisco border," Morena said.
Roch is Hispanic, 5 feet tall and weighs 180 pounds. He has gray hair, brown eyes and a scar across the top of his nose.
He was last seen wearing a beige San Francisco Giants baseball cap, a green windbreaker and blue pants, and he carried a cane, police said. He was also wearing an identification bracelet on his right wrist.
Anyone with information on Roch's whereabouts is urged to contact Daly City police at (650) 991-8119.