Les Cousins was opened on Friday 16 April 1965 in a basement venue at 49 Greek Street
, Soho which had earlier served as a 1950s skiffle club. Upstairs was the Dionysus restaurant owned by a family called Matheou, whose son, Andy Matheou ran the basement club. The club was reputed to have taken its name from Claude Chabrol’s 1959 film Les Cousins, the story of a young man from the country who comes to the city to study law, but is distracted by the rowdy cousin with whom he shares lodgings.
The club was noted for its all-night sessions and was favoured by the innovative musicians who were less welcome in more purist traditional folk clubs.
Noel Murphy was the first resident musician and compere. Other residents included Alexis Korner and Roy Harper.
Les Cousins was described by Roy Harper as "a spawning ground" for musical talent. In similar vein, Ian Anderson (editor of fRoots) said "...the music got so exciting, ’cause everybody listened to everybody else. So although you might choose to just play one thing, at the same time, you had an open mind for something else."
Roy Harper recorded his album Live At Les Cousins there, 30 August 1969 and The "Spontaneous Music Ensemble" (John Stevens and Evan Parker plus Peter Koward) also recorded there in 1967.
In 1970 a compilation LP 49 Greek Street was released, featuring artists associated with the club such as Synanthesia, Keith Christmas, Andy Roberts, Robin Scott, Tin Angel, Al Jones, Mike Hart and Nadia Cattouse, although most of the tracks were studio recordings. According to Emma Matheou whose father ran the club, the door depicted on the cover is from another address in Greek Street