Background: Previous studies on asthma mortality and hospitalizations in Réunion indicate that this French territory is particularly affected by this condition. Epidemiological studies conducted in schools also show higher prevalence rates in Réunion than in mainland France. However, no estimates are available on the prevalence of asthma among adults. In 2016, a cross-sectional survey was conducted to estimate the prevalence of asthma and to identify its associated factors in the adult population of Réunion. Methods: A random sample of 2,419 individuals, aged 18–44 years, was interviewed by telephone using a standardized, nationally validated questionnaire. Information was collected on respiratory symptoms, descriptions of asthma attacks, and triggering factors for self-reported asthmatics, as well as data on the indoor and outdoor home environment. "Current asthma" was defined as an individual who, at the time of the survey, reported having had asthma at some point in their life, whose asthma had been confirmed by a doctor, and who had experienced an asthma attack in the past 12 months or had been treated for asthma in the past 12 months. "Current suspected asthma" was defined as an individual presenting, in the 12 months preceding the study, clusters of symptoms suggestive of asthma consistent with the literature. Results: the estimated prevalence of asthma was 5.4% [4.3–6.5]. After adjustment, women, obesity, a family member with asthma, tenure in current residence, and the presence of indoor home heating were associated with asthma. The prevalence of symptoms suggestive of asthma was 12.0% [10.2–13.8]. After adjustment, marital status, secondhand smoke exposure, use of insecticide sprays, the presence of mold in the home, and external sources of air pollution were associated with the prevalence of suspected asthma. Conclusion: Preventive measures, including asthma diagnosis, promotion of individual measures to reduce risk exposure, and the development of studies to improve knowledge about indoor air allergens, are recommended.