The present invention relates to a process for purifying monomers, by evaporating at least a portion of the monomers present in a starting composition and then condensing it, which is characterized in that at least a portion of the starting composition is evaporated in a short-path evaporator, the mass flow density of the vapours {dot over (m)} being selected according to the relation (I) m . ≤ 1800  kg · K mbar · m 2 · h · kg kmol · p i · ( M ~ T ) 0.5 ( I ) in which {tilde over (M)} is the average molar mass of the vapours in the short-path evaporator in kg/kmol T is the temperature of the vapours in K pi is the pressure in the short-path evaporator in mbar {dot over (m)} is the mass flow density of the vapours in kg/(m2·h). A further aspect of the present invention is a plant for performing the process.