The Doctor of Myddfai is an opera in two acts composed by Peter Maxwell Davies to a libretto by David Pountney.

The work premiered at the New Theatre in Cardiff on 5 June 1996, performed by the Welsh National Opera and conducted by Richard Armstrong.

The opera takes place in a totalitarian society similar to that envisioned in Orwell's 1984, with a supreme ruler, mechanistic bureaucracy and endless war.

Background legend A shepherd fell in love with beautiful girl who appeared in Llyn y Fan Fach, a lake where he was tending his flock.

The opera The Doctor is worried about a strange new disease that has broken out and retells the legend to his Child.