The formation of extremely high aspect ratio CdSe nanorods (30:1) as well as arrow-, teardrop-, tetrapod-, and branched tetrapod-shaped nanocrystals of CdSe, has been achieved by growth of the nanoparticles in a mixture of hexylphosphonic acid and trioctylphosphine oxide. The most influential factors in shape control are the ratio of surfactants, injection volume, and time-dependent monomer concentration.