The epidemiological surveillance provides opportunities to know the magnitude and determinants of nosocomial infection and permits, at the same time, the planning, implementation and evaluation of prevention and treatment activities in order to approach the rates of infection in the hospital, as near as possible, to the irreducible minimum. We show data collected by surveillance system Guadalajara General Hospital from 1982 to 1987. In order to analyze general trends, seasonality, accidental variations and endemic levels, we have used statistical methods as linear regression, chi 2, equality proportions and built of an endemic channel with confidence intervals of 95%. We have observed a decreasing trend, locating endemic levels around to 4% of monthly accumulated incidence. There is a possible seasonal influence concurring with holidays periods and someone accidental variation over that we expected, it was related with a deteriorated situation about medical care.