Obstructive Sleep Apnea Syndrome (OSAS) and Asthma are two diseases with a high epidemiological impact that may coexist in some patients with the name of Alternative Overlap Syndrome. Both diseases have underlying pathogenic mechanisms (chronic inflammation, genetic predisposition etc). Epidemiological data suggest that the coexistence of OSA and asthma, also known as “Alternative Overlap Syndrome” has an adverse impact on health outcomes. Asthma and OSA overlap with similar comorbidities and underlying pathophysiology, potentiating the two conditions. The most common comorbidities associated with both diseases are Gastro-Esophageal Reflux Disease (RGE), rhinosinusitis and obesity. Neuromechanical reflex bronchoconstriction, local and systemic inflammation, the indirect effect on dyspnea of OSAS-induced cardiac dysfunction, angiogenesis and leptin-related airway changes may all play a common mechanistic role linking both disorders.