Monte Carlo simulations are widely used in analysis of interference between radiocommunication systems. Nevertheless, there is no formalization about the number of events necessary to run a simulation. In practice, this is often done based on the intuition of the engineer about the model. In this paper, we propose how to choose a number of events for Monte Carlo simulations. We address this issue by understanding that protection criteria for radiocommunication systems are usually related to a quantile of the result, and then calculating the number of events for which it is also possible to estimate a confidence interval for it. Results show that, for a confidence level of 99.9%, it is possible to estimate confidence intervals for p-quantiles for p up to 99.89% with 10,000 events.