We study the relation between the chirality of a discotic mesogen and that of the chiral columnar aggregates that they can spontaneously form by self-assembly. We discuss first the different types of chiral columns that can be in principle obtained. We introduce then a simple two-site Gay-Berne dissymmetric molecular model where chirality can be easily varied and perform extensive NPT Monte Carlo simulations of samples of these particles for different chiralities. At low temperatures we find nematic discotic and columnar mesophases formed by overall chiral columns and we analyze the results in terms of suitably defined observables and chiral correlation functions. We find that, at least for our model system, the columnar chirality is not originating from a regular helical or spiral arrangement of particles but it is mainly due to one-particle high-chirality defects separated by low-chirality domains. (C) 2003 American Institute of Physics.