The present invention relates to a process for the solidification and stabilization of concentrated aqueous sodium hydroxide solution, characterized in that the following steps are carried out: a) a hydraulic binder containing blast furnace slag is mixed with said sodium hydroxide solution, in the presence of at least one additional source of calcium ions and/or magnesium ions and/or silica, to form a slurry, and b) the slurry is left to set to a solid product. The invention further relates to the solid product obtained by carrying out the process of the invention. The invention can be applied to the treatment of sodium hydroxide solutions that are radioactive or contaminated by other pollutants.