Background and objective: The role of indoor air pollution as a risk factor for asthma and respiratory symptoms in middle age is unclear. We investigated associations between indoor air pollution sources and (i) asthma phenotypes and (ii) asthma-related respiratory symptoms in middle-aged adults. Methods: Subjects (n = 5729) who participated in the 2004 survey of the Tasmanian Longitudinal Health Study completed respiratory and home environment questionnaires. Associations between indoor air pollution sources, and asthma phenotypes and asthma-related respiratory symptoms were estimated. Results: Recent mould in the home was associated with current asthma (odds ratio (OR) 1.26; 95 confidence interval 1.06-1.50), wheeze (OR 1.34; 1.17-1.54) and nocturnal chest tightness (OR 1.30; 1.12-1.51). Stratified by atopy and gender, recent mould was associated with current non-atopic asthma only in males (OR 3.73; 1.29-10.80). More rooms affected by mould were associated with significant trends for current asthma, wheeze and nocturnal chest tightness. Home environmental tobacco smoke was associated with doctor-diagnosed asthma (OR 1.25; 1.02-1.53), wheeze (OR 1.69; 1.41-2.03), nocturnal chest tightness (OR 1.54; 1.26-1.88), with current asthma only in non-smokers (OR 2.09; 95 : 1.30-3.35) and with current asthma only in males (OR 1.74; 95 : 1.25-2.42). Among heating appliances, reverse cycle air conditioning was negatively associated with doctor-diagnosed asthma (OR 0.84; 0.70-1.00). Neither electric nor gas stove use was associated with either asthma phenotype or with asthma-related respiratory symptoms. Conclusions: In middle age, reducing home exposure to mould and environmental tobacco smoke might reduce asthma and asthma-related respiratory symptoms.