The principal aim of this study was to analyse the incidence of disease due to general and more specific causes among over 100,000 horses covered by complete insurance for veterinary care by a Swedish insurance company during 1997 to 2000. The database was used to calculate the rate of cause-specific morbidity in horses of different ages, sexes and breed groups kept in different regions with different human population densities. The joints were the most commonly affected part of the body, followed by unspecified/whole body, the skin and the digestive system. The most common specific diagnosis was fetlock arthritis, followed by lameness of undefined origin, other locomotor problems, traumatic injuries to the skin, arthritis in several joints, and colic. Geldings had the highest rate of at least one disease event in the joints, unspecified/whole body, skeletal or respiratory system, whereas in the other four major systems the difference between the sexes was marginal.