IMPORTANCE: There is growing awareness of the US health sector's substantial contribution to the country's greenhouse gas (GHG) emissions, exacerbating the health threats from climate change. Reducing health care's environmental impact requires understanding its carbon emissions, but there are few published audits of health systems and fewer comprehensive emissions analyses at the clinic or department level. OBJECTIVE: To quantify the annual GHG emissions from a large outpatient dermatology practice, compare relative sources of emissions, and identify actionable targets. DESIGN AND SETTING: This quality improvement study involving a comprehensive carbon footprint analysis (scopes 1-3) of a large (nearly 30 000 visits/y), outpatient medical dermatology practice within the University of Pennsylvania's academic medical complex was conducted following the GHG Protocol Corporate and Corporate Value Chain reporting standards for fiscal year 2022 (ie, July 2021 through June 2022). Data were obtained through energy metering, manual audits, electronic medical records, and administrative data. EXPOSURE: Data were converted into metric tons of carbon dioxide equivalent (tCO2e), allowing comparison of global-warming potential of emitted GHGs. MAIN OUTCOMES AND MEASURES: Primary outcomes were tCO2e by scope 1 (direct emissions), scope 2 (indirect, purchased energy), and scope 3 (indirect, upstream/downstream sources), as well as by individual categories of emission sources within each scope. RESULTS: Scope 3 contributed most to the clinic's carbon footprint, composing 165.5 tCO2e (51.1%), followed by scope 2 (149.9 tCO2e [46.3%]), and scope 1 (8.2 tCO2e [2.5%]). Within scope 3, the greatest contributor was overall purchased goods and services (120.3 tCO2e [72.7% of scope 3]), followed by patient travel to and from the clinic (14.2 tCO2e [8.6%]) and waste (13.1 tCO2e [7.9%]). Steam and chilled water were the largest contributors to scope 2. Clinic energy use intensity was 185.4 kBtu/sqft. CONCLUSIONS AND RELEVANCE: In this quality improvement study, the composition of emissions at the clinic level reflects the importance of scope 3, paralleling the health sector overall. The lower-resource intensity of the clinic compared to the average energy requirements of the total clinical complex led to a relatively large contribution from scope 2. These findings support efforts to characterize high-yield emissions-reduction targets and allow for identification of actionable, clinic-level steps that may inform broader health system efforts.