The polysomnographic examination is the basic test that allows changes in the physiological activities of the human body during sleep to be recorded. In the hands of a specialist, it is an indispensable tool for the diagnosis of many sleep disorders (including snoring, narcolepsy, somnambulism and others). A great deal of information can be gleaned from the study, but only the ability to interpret it logically allows conclusions to be drawn that are important for health. What are the recording parameters, ranges of variables and which data are important for the doctor interpreting the study?