A method for forming a cooling hole extending from an inlet on a first surface of a wall to an outlet on a second surface of the wall includes forming a diffusing section of the cooling hole, and a trailing edge on the outlet by electrical discharge machining, and forming longitudinal lobes in the diffusing section. The metering section extends from the inlet on a first surface of the wall towards the second surface of the wall. The diffusing section extends from the outlet to one end of a metering section located between the inlet and the outlet. The outlet is substantially linear or convex at the trailing edge and the lobes are separated by longitudinal ridges.