A cook arriving to open the theater's restaurant around spotted smoke and fire around 7 a.m. Sunday, the Madison Fire Department said.
The fire caused an estimated $100,000 in damage. In April, the 76-year-old building had $20,000 in damage when an alleged arsonist set a fire in a first-floor bathroom.
Fire officials had not yet said what might have caused Sunday's fire.
Orpheum owner Henry Doane initially rejected the arson finding in April's fire but now believes both fires were deliberately set.
``I'm part angry and part saddened,'' Doane said. ``I just don't understand why somebody would do something like this, if it was indeed arson.''
Fire officials said the theater suffered heavy smoke, fire and water damage on its first floor, and smoke damage throughout.
Jim Draeger, architectural historian for the Wisconsin Historical Society, said the Orpheum is ``irreplaceable.''
``To lose a theater like that would be a devastating thing for Madison,'' Draeger said. ``It's really a period piece. It's a treasure in the city of Madison.''
The theater seats up to 1,700 people in its main theater and hosts both live acts and movies.
The Orpheum already has been struggling financially. Madison Gas and Electric Co. sued the theater in September for $29,993 in outstanding bills.
The theater was closed for the month of June because of construction of the Overture Center for the Arts, and Doane has said he owed studios for films.
