A flexible cage of a rolling bearing belonging to a wheel hub assembly for motor vehicles, having a substantially circular rib and a plurality of fingers which extend from a side of the rib and have a base portion, the rib and the fingers having partially spherical concave surfaces defining together a plurality of partially spherical cavities for retaining respective rolling bodies. The rib has substantially straight portions, each of them integrally connected to a base portion of a finger, substantially oblique portions and protrusion portions.