Provided is a method of detecting a leak in a hydraulic cylinder of a rotor blade pitch system of a wind turbine including a plurality of rotor blades, which method includes the steps of selecting one of the pitch systems to undergo a functionality test; actuating a fluid pump to move the pistons of the hydraulic cylinders of the pitch systems to their outermost positions; monitoring the hydraulic cylinder pressure levels of the non-selected pitch systems while performing the functionality test on the selected pitch system; and analyzing the monitored hydraulic cylinder pressure levels of the pitch systems to detect a drop in pressure in a pitch cylinder of a non-selected pitch system. A leak detection arrangement of a pitch-controlled wind turbine; and a pitch-controlled wind turbine are also provided.