The clinically ill bird is often presented to the avian veterinarian with a variety of signs that are often vague. They include lethargy, weight loss, poor feathering, and loss of condition. The avian practitioner at this time begins to take a history and do a physical examination. In reaching a good definitive diagnosis, one aspect of avian disease is often overlooked. Improper nutrition is one of the most prevalent problems in avian medicine today. The practitioner must realize that a particular disease may be the result of a nutritional deficiency. Proteins, fats, carbohydrates, vitamins, and minerals are essential elements in the diet of a healthy bird. When a deficiency occurs, the body's ability to resist disease is damaged. Nutritional deficiencies are also a sequelae to systemic diseases. When a bird is ill, its feed intake declines, therefore, its requirement for basic nutrients is not satisfied. Proper nutrition of the ill bird is essential for prompt recovery from other systemic illnesses. Hence, primary systemic disease and nutritional deficiency often occur simultaneously.