Background: Studies have identified function pattern in obesity. Obesity's pathologies, both contributive and causal, continues to be the subject of much research and analysis. These associations, often complicating the identification of the underlying clinical diagnosis, warrant special consideration in light of the growing obesity epidemic. Objectives: A review of published literature to describe the major effects of obesity on pulmonary function and its interaction with respiratory pathophysiology, in order to provide a differential diagnostic tool for clinicians. Results: A distinctly restrictive respiratory pattern is identified in the obese, evident by markedly reduced lung volumes, particularly the expiratory reserve volume (ERV). This is attributed to decreased chest wall compliance, and impaired respiratory muscle function. There is some degree of airflow impairment seen in obesity not attributable to decreased lung volumes, shown by decreased expiratory flow rates. The association between chronic obstructive lung disease and obesity is not well defined. Obesity and asthma are shown to have a stronger correlation, which may in part be due to mechanical, immunological, and a variety of other mechanisms. Conclusions: Clinicians must consider the degree of obesity and other objective data such as pulmonary function profiles in the diagnosis and treatment of obese patients exhibiting symptoms of respiratory compromise.