Highly monodisperse CdSe nanocrystals were prepared in a three-component hexadecylamine-trioctylphosphine oxide-trioctylphosphine (HDA-TOPO-TOP) mixture. This modification of the conventional organometallic synthesis of CdSe nanocrystals in TOPO-TOP provides much better control over growth dynamics, resulting in the absence of defocusing of the particle size distribution during growth. The room-temperature quantum efficiency of the band edge luminescence of CdSe nanocrystals can be improved to 40-60% by surface passivation with inorganic (ZnS) or organic (alkylamines) shells.