The goal of this paper is to provide a controller design for a high-purity distillation column where the effect of uncertainties is taken into account. A structured uncertainty model has been developed which describes the dynamics of the high-purity distillation column for the entire operating range. Further, a two-point composition control scheme using the LV-configuration is applied which yields acceptable performance specifications. The structured singular value (mu) is used as a tool for evaluating the achievable control performance which is defined in terms of the H-infinity-norm of the weighted sensitivity function. In addition, a decentralised PID controller based on internal model control (IMC) scheme that is optimally tuned is found to be robust. The results of simulations show good disturbance rejection and set-point tracking for the controller. (c) 2006 Elsevier Ltd. All rights reserved.