Along with the Ascending Moonshine Dervishes and the Descending Moonshine Dervishes, the Persian Surgery Dervishes represent Terry Riley's move, in the early '70s, toward a compositional style characterized by greater intuitive expressiveness and more improvisatory execution. The piece is based on figurational patterns drawn from Riley's Keyboard Study No. 2, the theme expanded from four to five notes and repeated to create a 40-beat, left-hand pattern in which the shifting rates of speed in the right hand fall into and out of alignment. The ebbing, swirling feel of this multivalent rhythmic texture synergistically combines with the piece's employment of time-lag tape delay, which layers the already polyphonic texture onto itself. Riley's use of just intonation also serves to create a mood that is at once disorienting and satiating, exotic, and introspective. ~ Jeremy Grimshaw, All Music Guide
