A surfactant-assisted route in aqueous media has been shown to be suitable to prepare either individual primary CoFe2O4 nanocrystals or secondary spherical nanoporous assemblies with a high surface area. The formation of primary nanoparticles or of spherical assemblies is found to be dependent on the presence of the surfactant and on the particle size, but is shown that the nanoparticle-surfactant interface plays a dominant role. The size of the primary CoFe2O4 particles is controlled by the type of salt, the synthesis temperature and the concentration of the precursors. A detailed characterization evidences the shape and size of the primary particles, the way in which the primary particles assemble and their features in terms of morphological, textural and magnetic properties. (C) 2009 Elsevier Inc. All rights reserved.