Powders of CdSe nanoparticles were prepared by a pulsed sonoelectrochemical technique. The crystal size could be varied from X-ray amorphous up to 9 nm (sphalerite phase) by controlling the various electrodeposition and sonic parameters. The mechanisms for the effects of the various parameters on particle size are discussed. Optical properties of the powders were measured by diffuse reflection spectroscopy and the measured increase in band gap due to size quantization correlated with particle size.