Abstract: The invention relates to a process for preparing trioxane and at least one comonomer for preparing (co)polymers based on trioxane, in which, in a first step, formaldehyde the at least one comonomer reactant are reacted in aqueous solution to give trioxane and comonomer, to obtain a reaction mixture A1 comprising trioxane, comonomer, formaldehyde and water, with or without comonomer reactant. In a second step, the reaction mixture A1 is distilled in a first distillation stage at a first pressure to obtain a stream B1 enriched in trioxane and comonomer and a stream B2 comprising essentially water and formaldehyde, with or without comonomer reactant. In a third step, stream B1 is distilled in a second distillation stage at a pressure which is above the pressure of the first distillation stage to obtain a stream C1 comprising trioxane, comonomer and water and a product stream C2 consisting essentially of comonomer and trioxane.