Fungal sinus disease represents a spectrum of five different clinico-pathological entities, each linked by a common process of sinonasal inflammation secondary to fungi. Fungal sinus infection can be classified as invasive or non-invasive. The diagnosis is usually made by a combination of CT, histology and mycology features. Each type of fungal sinus infection has an individual clinical presentation, prognosis and options for treatment. Invasive infection typically occurs in an immunocompromised host and is characterised by histological destruction of tissue. Mortality rates remain high, and early detection and treatment are vital. Non-invasive fungal infections are classically more indolent and patients are usually treated for extended periods as chronic sinusitis before the condition is recognised.