Communication: The one-step synthesis of "core-shell" vesicle analogues using sonochemistry is described. The formation of such vesicles generally occurs in two steps-either the inorganic core is formed first, around which the shell is generated, or the empty shell is used as a microreactor for the crystallization of the inorganic core. Here ultrasound irradiation is used to simultaneously decompose Fe(CO)(5) and form siloxane polymer chains from (CH3)(3)SiCl to produce micrometer-dimension vesicles containing monodisperse spindles.