Neighboring districts are (from the west clockwise):
Khuan Don and
Khuan Kalong of
Satun province;
Khlong Hoi Khong,
Hat Yai, and
Na Thawi of Songkhla Province. Southwest of Sadao's 85 kilometre border with Malaysia are the Malaysian states of
Kedah and
Perlis. The district marks the southern end of
Phetkasem Road, the longest road in Thailand, which runs from
Bangkok via
Hat Yai to the
border crossing at Danok (Thailand)–
Bukit Kayu Hitam (
Malaysia). Major roads connect this road with
Pattani (intersection at Khlong Ngae) and
Padangbesar with the intersection at Sadao town. Two main border crossings with Malaysia are in the district. The main crossing is at Danok with
Bukit Kayu Hitam on the Malaysian side. The crossing is the busiest land border crossing between Thailand and Malaysia.
Phetkasem Road is connected to Malaysia's
North-South Expressway at this border crossing. Another crossing is at
Padangbesar, with the Malaysian town of
Padang Besar in
Perlis on the Malaysian side. The main railway crossing between Malaysia and Thailand is also at Padang Besar. The Thai-Malaysian border is porous, with illegal crossing points frequently discovered by authorities. ==History==