The aims of this thesis were to determine if there is an association between damp housing and asthma and to investigate whether damp housing adversely influences asthma severity. Asthmatic subjects reported more damp in both their current (Odds Ratio 4.1, 95%CL 2.3 to 7.6) and previous (Odds Ratio 1.9, 95%CI 1.1 to 3.2) dwellings than control subjects. The surveyor confirmed 112 (51%) dwellings to have evidence of damp and 57 (26%) evidence of visible mould growth. Dampness was detected in 58/90 (64%) dwellings of asthmatic subjects compared with 54/132 (41%) dwellings of control subjects (Odds Ratio 2.62, 95%CI 1.50 to 4.55). There was an increasing prevalence of damp in the dwelling with increasing severity of asthma. This association could not be explained by potential bias in study design and persisted after controlling for socio-economic and other confounding variables (adjusted odds ratio 3.03, 95% CI 1.65 to 5.57). Asthma severity scores correlated statistically with measures of total damp (r=0.30, p=0.006) and visible mould growth (r=0.23, p=0.035) in the dwelling. Patients living in homes with evidence of damp had a lower FEV₁ (mean difference 10%, 95% CI 1.0 to 20) and a lower FEV₁/FVC ratio (mean difference 5.4%, 95% CI -0.1 to 10.9) than patients living in dry dwellings. These associations persisted after controlling for unemployment, household income and cigarette smoking. Asthma is significantly associated with living in damp housing. Measures of asthma severity, disability and airflow obstruction are higher in patients living in damp, mouldy dwellings. Effective measures to reduce the risk of damp and condensation occurring in dwellings are required to be incorporated into future housing design.