Here we study the effects of confinement on the self-assembly of diblock copolymers. Specifically, we study the hexagonal cylindrical phase as it self-assembles within a narrow confinement. We quantify the structural deformation of the cylindrical morphology that arises from the frustration that the narrow confinements exert on the system when the confinement width is incompatible with the lattice structure of the bulk mesophase. (C) 2004 Wiley Periodicals, Inc.