Equilateral CdS nanocrystals with 10-nm sides are produced in a Cd(AOT)(2)/isooctane/water reverse micellar solution. The structures of individual nanocrystals are determined by TENT and HRTEM, and these data were compared with computer simulations and power spectra calculations. This shows that the particles are crystallized in a hexagonal (wurtzite) form. The thickness of these equilateral nanocrystals (around 5 nm) is estimated from optical measurements. These nanocrystals are not highly stable as the coated surfactant desorbs, and they coagulate, forming particles with a cubic structure (zinc blende).