BACKGROUND: Urbanisation is an important contributor to the prevalence of asthma worldwide, and the burden of this effect in low-income and middle-income countries undergoing rapid industrialisation appears to be growing. We sought to characterise adult asthma prevalence across four geographically diverse settings in Peru and identify both individual and environmental risk factors associated with adult asthma. METHODS: We collected sociodemographics, clinical history and spirometry in adults aged >/=35 years. We defined asthma as meeting one of the three criteria: physician diagnosis, self-report of wheezing attack or use of asthma medications. We used multivariable logistic regression to assess individual and environmental factors associated with adult asthma. RESULTS: We analysed data from 2953 participants (mean age 55 years; 49% male). Overall asthma prevalence was 7.1%, which varied with urbanisation: highest in Lima (14.5%), followed by urban Puno (4.0%), semiurban Tumbes (3.8%) and rural Puno (1.8%). In multivariable analysis, being male (OR=0.60, 95% CI 0.39 to 0.93) and living at high altitude (OR=0.26, 95% CI 0.16 to 0.42) were associated with lower odds of having asthma, whereas living in an urban setting (OR=4.72, 95% CI 3.15 to 7.23) and family history of asthma (OR=1.83, 95% CI 1.19 to 2.73) were associated with higher odds. Current daily exposure to biomass fuel smoke (OR=1.18, 95% CI 0.70 to 1.91) and smoking (OR=0.99, 95% CI 0.73 to 1.22) were not associated with asthma. CONCLUSIONS: These findings confirm that urbanisation is an environmental risk factor of asthma, questions biomass fuel smoke exposure as an important risk factor and proposes high altitude as possibly protective against the development of asthma.