<p>Hypersensitivity pneumonitis (HP) refers to the inflammatory lung condition that arises from inhalational exposure to various (mostly organic) antigens with the development of lymphocytic alveolitis and granulomatous pneumonitis. A myriad of antigens have been implicated and the list continues to grow. The clinical features are varied, implicated antigens protean, and the investigations complementary in making a diagnosis, but the condition remains a difficult one to diagnose, mostly due to a lack of clinical suspicion. In this article we discuss HP, its aetiology, clinical features as well as diagnosis and management.</p>