Background The diagnosis of COPD is made by objectively demonstrating nonreversible airflow obstruction of the lungs. Despite this, rates of pulmonary function testing (PFT) for diagnosis remain low. It is still not known why testing is underused. Methods We conducted a population study using the health administrative data of all individuals 35 years of age and older newly diagnosed with COPD in Ontario, Canada, between 2000 and 2010. Receipt of PFT during the peridiagnostic period (between 1 year before and 1 year after a diagnosis of COPD) was determined and related to patient demographic and clinical characteristics as well as primary care physician and health-care system factors. Results Only 35.9% of the 491,754 Ontarians newly diagnosed with COPD during the study period received PFT. Individuals diagnosed before age 50 years or after age 80 years, those living in long-term care, and those with stroke and/or dementia were less likely to receive testing. Patients who had a medical specialist involved in their care and/or had other coexisting pulmonary disease were more likely to receive testing. Finally, older primary care physicians were less likely to order testing for their patients. Conclusions Only about one-third of individuals with COPD in Ontario, Canada, received PFT to confirm their diagnosis; age, comorbidity, and physician factors appear to influence its use. Targeted strategies that address these factors could increase the rate of appropriate testing of people with suspected COPD and improve quality of COPD care.