Maricopa County Supervisor Max Wilson says he's resigning, effective on March 11.
The 70-year-old Litchfield Park Republican is stepping down because of health reasons.
His chief of staff said Friday that Wilson was hospitalized with the flu in January and hasn't fully recovered yet.
The Arizona Republic says Wilson has had open-heart surgery at least once since joining the supervisors.
Wilson has been on the board since 2002. He won his full third term on the board last November.
He oversees District 4 which includes Sun City, Sun City West, Litchfield Park, Surprise, El Mirage, Peoria, Youngtown, Wickenburg and parts of Glendale, Goodyear, Avondale and Buckeye.
Officials say the board will select Wilson's replacement, who must be a registered Republican from District 4.