Obstructive lung diseases (OLD) such as asthma and chronic obstructive pulmonary disease (COPD) are very prevalent conditions. Disease phenotypes (e.g. chronic bronchitis, emphysema, etc.) often overlap, and significant confusion exists about their optimal nosologic characterization. Obstructive sleep apnoea (OSA) is also a common condition that features bidirectional interactions with OLD. OSA appears to be more commonly seen in patients with OLD, perhaps as a result of shared risk factors, for example obesity, smoking, increased airway resistance, local and systemic inflammation, anti-inflammatory therapy. Conversely, OSA is associated with worse clinical outcomes in patients with OLD, and continuous positive airway pressure therapy has potential beneficial effects on this vicious pathophysiological interaction. Possible shared mechanistic links include increased parasympathetic tone, hypoxaemia-related reflex bronchoconstriction/vasoconstriction, irritation of upper airway neural receptors, altered nocturnal neurohormonal secretion, pro-inflammatory mediators, within and inter-breath interactions between upper and lower airways, lung volume-airway dependence, etc. While the term overlap syndrome has been defined as the comorbid association of COPD and OSA, the interaction between asthma and OSA has not been integrated yet nosologically; in this review, the latter will be called alternative overlap syndrome. In an effort to bolster further investigations in this area, an integrated, lumping nomenclature for OSA in the setting of OLD is proposed here--OLDOSA (obstructive lung disease and obstructive sleep apnoea) syndrome.