Abstract: An integrated process for preparing trioxane from formaldehyde, comprising the steps of: a) feeding a feed stream A1 comprising formaldehyde and water and a recycle stream B3 comprising predominantly water and additionally formaldehyde and trioxane to a formaldehyde concentration unit and separating it into a formaldehyde-rich stream A2 and a stream A3 consisting essentially of water; b) feeding a product stream C1 comprising trioxane, water and formaldehyde, a recycle stream E1 comprising trioxane, water and formaldehyde, and, if appropriate, the stream A2 to a first low-pressure distillation column and distilling at a pressure of from 0.1 to 1.