Recognizing the causes behind phenomena highlights from a historical perspective that scientists, thinkers and healers have always paid significant attention to the laws of the relationship between nature and human beings. Their curiosity was followed by precise observation and logical reasoning, which has always been present in the life of mankind. Since billions of individuals (organisms) in the living world act countless as pathogens on the human race, it was recognized soon that certain diseases develop or can develop by the impact of the environment, although specific causes were not yet realized people were aware of mass occurrences. This study provides a brief summary of the developing epidemiology and its closely related statistics.  Kulcsszavak: járványok, statisztika, folyamatok vizsgálata, orvosi megfigyelések