PURPOSE: This case-control study was undertaken to elucidate the controversy concerning whether low-level, long-term exposure to non-sensitising air pollution at workplaces may cause asthma. METHODS: A case-control study of 192 adult-onset asthma cases aged 20-65 years and 323 controls was conducted in the southeast of Sweden. Cases were identified from computerised registers from the region, diagnosed 2000-2004 and diagnoses were confirmed via medical files. Referents were randomised from the population register of the region. Exposure was monitored by a 16-page questionnaire. Special attention was devoted to identifying and in the final analyses excluding subjects exposed to sensitising agents. RESULTS: Three years or more of occupational exposure to air pollution from dust, smoke, fumes or vapours before the year of diagnosis by analyses adjusting for age yielded an increased risk for asthma (OR = 2.3, 95% CI 1.2-4.2) in men, while in women, no risk was seen. In a multiple logistic regression analysis in men without allergy in childhood, a significant risk was seen (OR = 2.8, 95% CI 1.07-7.4), when subjects exposed to identified allergens were excluded. In women, no excess risk was observed from occupational air pollution. CONCLUSION: The results of this study support an association between occupational exposure to low level non-sensitising air pollution and adult-onset asthma in men.