The invention relates to a process for preparing trimethylolpropane with simultaneous formation of formate salts of the formula M(OOCH)n  (I), where M represents the alkali metals lithium, sodium, potassium, rubidium, caesium and/or the alkaline earth metals beryllium, calcium, strontium, barium and n is 1 when M is an alkali metal and is 2 when M is an alkaline earth metal, where n-butyraldehyde, formaldehyde and a base are reacted by the inorganic Cannizzaro process and the reaction mixture formed is subjected to vapour pressure filtration as a suspension, if appropriate after partly removing distillable constituents, such as water.