Long-term observations of photoluminescence at the single-molecule level were until re-cently very difficult, due to the photobleaching of organic fluorophore molecules. Al-though inorganic semiconductor nanocrystals can overcome this difficulty showing very low photobleaching yield, they suffer from photoblinking. A new marker has been re-cently introduced, relying on diamond nanoparticles containing photoluminescent color centers. In this work we compare the photoluminescence of single quantum dots (QDs) to the one of nanodiamonds containing a single-color center. Contrary to other mark-ers, photoluminescent nanodiamonds present a perfect photostability and no photoblink-ing. At saturation of their excitation, nanodiamonds photoluminescence intensity is only three times smaller than the one of QDs. Moreover, the bright and stable photolumines-cence of nanodiamonds allows wide field observations of single nanoparticles motion. We demonstrate the possibility of recording the trajectory of such single particle in culture cells.