Which traditional carol includes the repeated refrain "Fa la la la la, la la la la"?

The traditional carol with the repeated refrain “Fa la la la la, la la la la” is “Deck the Halls.”

The melody comes from the Welsh winter and New Year tune “Nos Galan,” whose history reaches back well before the English Christmas lyrics. The Welsh air was published in the eighteenth century and is associated with New Year’s Eve, rather than being originally written as an English Christmas song.

Scottish musician Thomas Oliphant supplied the English words, first published in 1862 in Welsh Melodies. The lyrics combine festive imagery—holly, seasonal clothing, dancing, harps, and the old year—with the instantly recognizable “fa-la-la” refrain. The title was originally singular, “Deck the Hall,” before the plural “Deck the Halls” became common around 1892.

The refrain is not unique to Christmas music in origin: related “fa-la-la” syllables appear in older Welsh material. That is why the carol blends a Welsh New Year melody with later English holiday lyrics.