Introduction Outdoor atmospheric pollution seems to have a noticeable effect on the respiratory system, increasing of the prevalence of allergic respiratory diseases such as the asthma and the rhinitis. Purpose To determine fungal spore counts and their seasonal swings in the outdoor atmosphere of the city of Sousse, Tunisia during the year 2003. Materials and methods A volumetric Burkard © sensor was placed on the roof of the maternity service of the local hospital. Samples were sent every week to the European Bioclimatic Medical Center of Research and University Education (CEMBREU) for counting. The results were expressed as the number of fungal spores per cubic meter of air. The following meteorological data were recorded: relative humidity, mean annual outdoor temperature and mean annual rainfall. Results One hundred and sixty thousand and two hundred and ten fungal spores per cubic meter of air were detected in the outdoor atmosphere in Sousse. Four varieties of spores were observed: Alternaria, Cladosporium, Epicoccum and Botrytis. The maximum concentration of outdoor fungal spores was observed in spring. During this season, the density of Alternaria, Cladosporium and Epicoccum spores correlated in a positive and significant way with the temperature, which varied between 15°C and 25°C. Conclusion As a result of their high ambient concentrations, fungal spores could be considered to be an important etiological factor in allergic respiratory diseases including rhinitis and asthma.