Ground-state properties of a two-dimensional quantum dot composed of N electrons and an impurity are investigated by the Thomas-Fermi (TF) method at T = 0. The changes induced by the impurity in electron density, chemical potential and total energy are calculated. Calculations are also performed for different number of particles and strength of confinement. The results indicate that Thomas-Fermi approximation is applicable even when the system contains only a few particles. (c) 2005 Elsevier B.V. All rights reserved.