Aim: Questionnaires are a cheap means of studying large populations but the information obtained from them is seldom validated. Earlier studies have reported both high and low levels of agreements between inspectors' observations and occupants' reports regarding home environmental factors that included moisture problems. The aim of this study was to validate information received from a questionnaire survey regarding building characteristics, mouldy odour, and signs of moisture problems in 390 Swedish homes. Method: In a case control study on the association between home environmental factors and asthma/allergy among children, 390 homes were visited by trained inspectors for ocular inspection of visible moisture damage and perceptions of mouldy odour. Their observations were then compared with questionnaire reports collected 18 - 24 months earlier from the families. Results: A high level of agreement was found between the inspectors' observations and the occupants' questionnaire reports on technical parameters. This included type of house, type of ventilation system, and foundation, particularly in single-family houses. There was low agreement regarding vinyl or linoleum floor coverings and indications of dampness and mouldy odour. However, the stronger the mouldy odour experienced by the inspector, the higher the level of agreement. Conclusions: The questionnaire was a quite reliable source regarding technical parameters of the home but not for dampness problems. The questionnaire was better for predicting buildings without problems than detecting problems of mouldy odour and visible indications of moisture. To increase the validity of future questionnaires, simple drawings or information on critical spots for dampness could be used.