The paper adds to our knowledge of what non-executive directors do, knowledge which is still in its infancy. More specifically, it reports the findings of a survey among more than 250 Dutch non-executive directors regarding their roles and limitations. Although the majority agreed that monitoring is their main duty, they also expressed doubts whether they are really able to carry out this "watchdog role" effectively. The primary limitation is sought in the asymmetry of information which gives rise to the so-called "independence paradox": in obtaining adequate information non-executives are dependent on the executives they are expected to supervise and to be independent from. Copyright Blackwell Publishing Ltd. 2004.