Illness and disease occur when the natural balance of good health is upset. Illness may be caused by physical trauma, occur when any of the defence systems are overwhelmed or happen when the body is confronted with a challenge that evolution didn’t prepare it for. The nature of illness and disease is always changing. For example, before effective vaccines were widely available and when cats and dogs wandered freely, infection and trauma were the most common problems needing veterinary attention. Preventative vaccination and responsible pet ownership have changed the nature of disease. Today, genetic, metabolic, geriatric and new environmental disorders play dominant roles in what we see at the London Veterinary Clinic.