BACKGROUND: Socioeconomic status is known to influence the prevalence, severity and mortality of obstructive lung diseases, but it is uncertain whether it affects the use of diagnostic spirometry in patients initiating treatment for these conditions. The objective of this paper was to examine a possible association between education, income, labour market affiliation, cohabitation status and having spirometry performed when initiating medication targeting obstructive pulmonary disease. METHODS: We conducted a population-based cohort study. Danish national registers were linked, retrieving data on prescriptions, spirometry testing, socioeconomic and demographic variables in all first time users of medication targeting obstructive lung disease in 2008. RESULTS: A total of 37,734 persons were included and approximately half of the cohort had spirometry performed. Among medication users under 65 years of age, being unemployed was significantly associated with reduced odds of having spirometry performed, the strongest association was seen in men (OR = 0.82, CI = 0.73-0.91). Medium income was associated with increased odds of having spirometry performed in men (OR = 1.18, CI = 1.06-1.30) and high educational level (>12 years) was associated with reduced odds of having spirometry performed in women (OR = 0.86, CI = 0.78-0.94). Cohabitation status was not associated with having spirometry performed. Among medication users over 65 years of age, living alone was associated with reduced odds of having spirometry performed among men (OR = 0.78, CI = 0.69-0.88). CONCLUSION: Social inequity in spirometry testing among patients initiating medication targeting obstructive lung disease was confirmed in this study. Increased focus on spirometry testing among elderly men living alone, among the unemployed and among women with higher education is required when initiating medication.