A study was made of the indoor mycobiota in a range of public and private buildings (libraries, museums, laboratories and offices, warehouses, homes and a school) in the city of Havana (Cuba). Culturable airborne fungi were sampled using a slit-to-agar impactor (Chirana aeroscope). High levels of contamination were recorded, with more than 700 colony-forming units per cubic metre of air in 85% of the buildings sampled, and more than 1,000 in 55% of buildings. Of the 28 genera and 31 species identified, the most common were Aspergillus flavus, Aspergillus niger, Penicillium citrinum, Cladosporium cladosporioides and Cladosporium sphaerospermum. Genus and species diversity was analysed, and new findings were obtained regarding Cuba’s atmospheric ecosystem.