Systemic diseases may affect the oral tissues, i.e. oral mucosa, salivary glands, teeth or bone, and oral manifestations will frequently present early, i.e. in association with (non-fulminant) systemic disease. Thus, recognition and proper diagnosis is essential to initiate appropriate treatment schedules. Key examples of systemic disease groups with oral manifestations include dermatological, inflammatory connective tissue diseases, haematological and inflammatory gastrointestinal diseases, as well as neurological and endocrine diseases.