Due to the 1992 Barcelona Olympic Games some modifications were introduced in the epidemiologic surveillance system for infectious diseases in place in the city, in order to expand its coverage and shorten its timeliness in detecting outbreaks and investigating cases. These modifications were introduced for a group conditions (hepatitis, meningococcal disease, legionnaire's disease and food outbreaks), selected on the basis of incidence, time of the year, previous experience in other settings, and likelihood of outbreak occurrence. In the June-August 1992 period (Olympic period), no increases in the incidence of selected conditions were observed when compared to the same period in 1986 to 1991. Major changes were observed in the source of food outbreak reporting, with a large increase in outbreaks reported by emergency room departments. There was an increase in the number of domestic foodborne outbreaks and a reduction in those related with restaurants. Timeliness in the detection of cases was shortened. The use of similar modifications can be useful for epidemiologic surveillance systems in other comparable settings or occasions.