Sleep staging is one of the most important tasks on the context of sleep studies. For more than 40 years the gold standard to the characterization of patient’s sleep macrostructure was the set of rules proposed by Rechtschaffen and Kales (R&K) recently modified by AASM rules. Nevertheless the resulting map of sleep, the so-called hypnogram, has several limitations such as its low temporal resolution and the unnatural characterization of sleep through assignment of discrete sleep states. This study reports an automatic method for the characterization of the structure of the sleep. The method is based on the use of fuzzy inference in order to provide soft transitions among the different states. Main intention is to overcome limitations of epoch-based sleep staging by obtaining a more continuous evolution of the sleep of the patient.