Severe sepsis is an ongoing challenge for clinicians and health-care administrators mainly because is associated with a high incidence, mortality rate and costs. In recent years, several epidemiological studies about the incidence of sepsis have come out in different and prestigious journals. However, it is not advisable to draw direct conclusions from those studies considering methodological flaws or even different approaches. Hence, we have to be familiar with those obstacles and know how to overcome them. This review paper highlights the methods which have been used in these studies and depicts the results of occurrence rate or incidence of sepsis in countries and in intensive care units.