In the last few decades, several works on event related potentials (ERPs hereafter) during sleep have been reported. In spite of numerous studies, clear methodological rules for this kind of study are often missing, making it difficult to valorize the scope of these results. We propose here a description of methodological aspects to be considered when evaluating ERPs during sleep. The use of Rechtschaffen and Kales rules versus automatic methods is assessed, plus the additional use of certain quantitative measures. Additionally, two topics are discussed which must be controlled in ERPs sleep studies: the First Night Effect, and sleep disturbances. Better control of experimental paradigms is relevant for the growth of the neuroscience of sleep.