The invention relates to a method for producing a highly concentrated, gaseous formaldehyde with a molar ratio CH2O: H2O of = 0.6, from an aqueous formaldehyde solution, by evaporating at least part of said solution, the aqueous formaldehyde solution being heated to an evaporation temperature T and the gas phase formed being drawn off. According to the invention, the following formula holds good for the evaporation temperature T: T [ °C] = T'min [ °C] wherein T'min(c) = A + B x (c/100) + C x (c/100)2 + D x (c/100)3 and A = + 68.759, B = + 124.77, C = - 12.851, and D = - 10.095, c being the actual CH2O content of the aqueous formaldehyde solution during the evaporation in wt. %, amounting to between 20 and 99 wt. %.