The increasing problem of sensitization to Ambrosia pollen in Europe has stimulated studies on Ambrosia pollen occurrence and pollinosis in Croatia. The aim of this study was to analyze the ragweed pollen pattern in Zagreb and to determine the incidence of sensitization to this pollen types in patients with seasonal respiratory allergy. The study was performed in the city of Zagreb during the 2002-2005 seasons. Skin prick test were performed on a total of 750 patients aged 18-80 in Zagreb between 2 January - 31 December 2004. The mean 4-year rate of ragweed pollen in the Zagreb atmosphere was 14.8% of all plant pollen. The highest rate of airborne ragweed pollen was recorded in August and September. 365 patients were allergic to ragweed pollen; 20.3% of them monosensitized; 10.9% allergic to Ambrosia and Artemisia pollen. Almost all study patients suffered the most severe symptoms in August and September. The highest proportion of allergic patients were recorded in the 31-50 age group and the lowest proportion in the >50 age group. Forecasting of allergenic pollen season in an area is a crucial pursuit for all developed countries, in order to minimize clinical symptoms in patients suffering from respiratory allergy. This can be achieved through public announcements by mass media (radio, television, internet, etc.) aiming to protect allergic individuals.