We show that if a hyperoval H of PG(2, q), q > 4, admits an insoluble group G, then G fixes a subplane π 0 of order q 0 > 2, H meets π 0 in a regular hyperoval of π 0 on which G ∩ PGL(3, q) induces PGL(2, q 0), and if H is not regular then q > q 2 0. We also bound above the order of the homography stabilizer of a non-translation hyperoval of PG(2, q) by 3(q − 1). Finally, we show that the homography stabilizer of the Cherowitzo hyperovals is trivial for q > 8.