A pop-up sprinkler is provided with an internally mounted and upwardly open debris cup for capturing debris such as dirt and pebbles falling into the sprinkler, to prevent such debris from contacting and interfering with an internally mounted rotary drive mechanism. The sprinkler includes a housing or case carrying a pop-up riser with a spray head thereon for projecting a stream of irrigation water over surrounding terrain and vegetation. The rotary drive mechanism includes a water-driven element such as a turbine coupled by a reduction gear unit or the like for rotatably driving the spray head in a manner sweeping the projected water stream over the surrounding terrain and vegetation. The debris cup is mounted within the sprinkler case generally at a lower end of a nozzle passage formed in the riser, and generally overlying the water-driven element, in a position to capture and retain debris falling into the sprinkler case through the nozzle passage.