We analyze the problem of the interplay of superconductivity and ferromagnetism, by focusing on their coexistence. The interest in this field has been renewed after the recent discovery of coexistence of superconductivity and ferromagnetism in UGe2, URhGe, ZrZn2, and in rutheno‐cuprate RuSr2RECu2O8compounds, with RE= Eu or Gd. In this paper we concentrate on the competition between itinerant ferromagnetism and singlet superconductivity looking at the case in which the same electrons participate in both the ordered phases. By using a mean field approximation, we have studied the stability of the coexistence phase when the ferromagnetic instability is described through the Stoner model, and when it can be ascribed to a kinetic exchange mechanism. © 2003 American Institute of Physics