The seasonal distribution of fungal spore concentration in the city of Porto, Portugal, was continuously studied, from 1 January to 31 December 2003, using a 7-day volumetric Burkard trap. In Portugal, aerobiological studies are scarce, and to our knowledge there are no published data on the atmospheric concentration of fungal spores. The aim of this work therefore is to initiate the aeromycological studies in Porto. The total airborne spore concentration fluctuated between 2 and 2,198 spores/m³ per day with an daily mean of 403 spores/m³. The highest airborne spore concentration was found during the summer and the early autumn, while the lowest concentration was registered during the winter. A range of allergenic and phytopathogenic fungal spores was present in the atmosphere of Porto throughout the entire year, although in different concentrations. Among the 22 fungal spore types identified Cladosporium (74.5%), Ganoderma (11.7%), Aspergillaceae (2.9%), Ustilago (2.5%), Coprinus (1.5%), Alternaria (1.3%) and Botrytis (1.3%) were the most frequent. Seasonally, spore levels of Cladosporium and Alternaria peaked in the autumn and winter, Ganoderma peaked toward autumn, whilst spore levels of the basidiomycete Coprinus fluctuated throughout the year. The total spore concentration was negatively correlated with wind speed and positively correlated with temperature and relative humidity.