  The structure of lamellar phases of symmetric $AB$ diblock copolymers in a
thin film is investigated. We quantitatively compare the composition profiles
and profiles of individual segments in self-consistent field calculations with
Monte Carlo simulations in the bond fluctuation model for chain length N=32 and
$\chi N=30$. Three film thicknesses are investigated, corresponding to parallel
oriented lamellae with 2 and 4 interfaces and a perpendicular oriented
morphology. Taking account of capillary waves, we find good quantitative
agreement between the Monte Carlo simulations and the self-consistent field
calculations. However, the fluctuations of the local interfacial position are
strongly suppressed by confinement and mutual interactions between lamellae.
