CdSe ultra-thin quantum wells (UTQWs) with thickness in the 0.5 to 4 monolayers (ML) range were grown by pulsed beam epitaxy (PBE) between barriers of ZnSe at substrate temperatures of 260 and 290 °C. In each sample, five similar QWs separated by barriers around 200 Å thick were deposited onto a 5000 Å buffer layer of ZnSe. During the growth process, the surface was monitored in-situ by reflection high energy electron diffraction (RHEED); a 2D growth mode was observed in all the UTQWs. The analysis of the streak positions in the RHEED patterns indicated a critical thickness around 1.5 ML. The photoluminescence (PL) experiments exhibited intense and narrow peaks in the blue-green region of the spectra. The energy of the PL peaks presented a clear dependence on growth temperature and QW thickness. The emission of the UTQWs grown at 290 °C was blue-shifted in comparison to those grown at 260 °C. The PL peaks of the samples show the presence of different transitions, which cannot be explained in terms of thickness fluctuations.