The health effects in teachers of a mold-damaged school before and during an extensive remediation process were assessed. Health data were collected with self-administered questionnaires from teachers (n=31) working in a moisture and mold damaged school and from the reference group of teachers (n=13) working in a non-damaged school. The questionnaire study was repeated three times. Spirometry was measured in 33 individuals in the spring 1997 and repeated in the spring 1999 and 2000. In the damaged school, a cluster of eight asthma cases was identified, the prevalence of asthma being 26%. Before the remediation, the number of sinusitis episodes was higher (p=0.040) and the mean duration of sick leaves longer (p=0.015) among the study group than in the reference group. A higher prevalence of hoarseness and perceived poor quality of indoor air were reported. During the follow-up, no new asthma cases appeared. After the remediation, bronchitis, conjunctivitis, symptoms of allergic rhinitis and the sum of respiratory infection episodes decreased significantly. Some of the asthmatics had low values in the spirometry but no changes in the lung function were observed at the group level. The remediation of the mold damage had beneficial effects on teachers' health.