Geriatric horses, like other animals (and humans), suffer from various diseases called old-age diseases. This publication has been developed in response to the needs of owners and caretakers of a growing number of geriatric horses. Since the horse has a long life span, the geriatric stage can encompass up to 1/3 of the animal’s lifetime and can quite often last more than 10 years. This paper aims at systematizing the information of the most prevalent geriatric diseases in horses which inhibit their performance and considerably lower their quality of life. Knowledge of these diseases can help to avoid mistakes when keeping and managing such horses and may provide guidelines for maintaining welfare and preventive treatments. This article reviews the most prevalent old age health problems, their origin, diagnostics, course and effects for the body. Information about the most common diseases of old age in horses is found in 119 references. The nine sub-chapters include the diseases of the digestive system, especially the oral cavity, the stomach and bowels’ diseases, the respiratory system, the cardiovascular system, dysfunctions of the locomotor system, eye diseases, endocrine and neuroendocrine diseases as well as the immune system, neoplasms and general body condition. It should be emphasized that there is the possibility to maintain the well-being of geriatric horses through progress in veterinary medicine and sharing knowledge of equine functioning and health protection. Preventive health care should include regular blood testing, regular dental check-ups and adequate nutrition adapted to the overall condition, dental condition, physical activity and comorbidities. Adequate individual supplementation recommended by a nutrition specialist and a veterinarian is also essential.