According to Official Guinness Records,
The longest dance marathon by a couple is 38 hr 30 min and was achieved by Brett and Jennifer Griswold (both USA) in Hawaii, USA, from 6 to 7 December 2014.Brett and Jennifer performed the Argentine Tango for the duration of their attempt. They are both dance instructors in Honolulu, Hawaii. The attempt was used to raise money for the National Federation of the Blind (NFB).
For a complete list of 2014 records, please visit 2014 Guinness Records in United States.