A process is provided for producing low sulfur diesel having a high cetane number where the temperature and pressure requirements for obtaining low levels of sulfur is separated from the temperature and pressure requirements for improving cetane. In one aspect, a low pressure hydrodesulfurization zone and a high pressure aromatic saturation zone are employed to sequentially achieve the desired sulfur and cetane levels. In another aspect, the process first converts a diesel boiling range hydrocarbonaceous stream in a hydrotreating zone at conditions effective to produce a hydrotreating zone effluent having a reduced concentration of sulfur with minimal saturation of aromatics. Hydrogen is then admixed with the hydrotreating zone effluent, which is then reacted in a substantially liquid-phase continuous reaction zone substantially undiluted with other streams to effect saturation of aromatics to provide a liquid-phase continuous reaction zone effluent having an improved cetane number.