Introduction: This article presents an assessment of the quality of spirometry tests and an initial estimate of the prevalence of obstructive ventilatory dysfunction (OVD) among the first participants in the Constances study. Methods: Constances is an epidemiological cohort consisting of randomly selected volunteers aged 18 to 69 years at enrollment. Spirometry tests (flow-volume curves without bronchodilation testing) were performed according to a standardized procedure. Their quality was assessed by two pulmonologists on a sample of curves deemed usable by the operator. The prevalence of OLD was estimated among adults aged 30 to 69 years recruited as of January 31, 2014, who had a usable spirometry test. LOB was defined as a FEV1/FVC ratio <0.70. Results: Spirometry results deemed usable by the operator were acceptable or optimal for 99% of the spirometry sample studied. Among the 28,315 participants aged 30 to 69 years at the time of the health examination, 15,206 (53.7%) had an acceptable spirometry result; 5.6% of them (men: 7.7%; women: 3.8%) had a TVO. Conclusion: Quality control confirmed that spirometry tests judged to be of good quality by the operator were acceptable. However, only 53.7% of participants had a usable spirometry test, confirming the difficulty in performing the test optimally. The FEV1/FVC ratio was less than 0.7 in 5.6% of adults aged 30 to 69 years.