This work was conducted in order to study how the health of adults is affected by the presence of moisture or mould in the home. A random sample of 310 houses in Finland was studied during the years 1993-1994. The houses were investigated for visual signs of moisture by a surveyor, and observations of mould were reported by the occupants. A moisture problem was observed in 52% and a mould problem in 27% of the houses. Health data was collected by means of a postal questionnaire from 699 adults. Exposure to moisture was significantly associated with sinusitis, acute bronchitis, nocturnal cough, nocturnal dyspnoea and sore throat, and the exposed inhabitants had significantly more episodes of common cold and tonsillitis. Exposure to mould was significantly associated with common cold, cough without phlegm, nocturnal cough, sore throat, rhinitis, fatigue and difficulties in concentration. Building-related moisture or mould increased the risk of upper and lower respiratory infections and symptoms as well as of nonrespiratory symptoms.