Diastema (pleural diastemata) is the most common disorder predisposing the horse to periodontal disease. These can affect the incisors or cheek teeth but pose more significant problems in the cheek teeth. Cheek teeth diastema can be congenital or develop secondary to other pathology. This condition is underdiagnosed in clinical practice due to lack of awareness of its seriousness and also due to poor dental examination techniques. A thorough dental examination requires both digital palpation and visual inspection of the oral cavity. Proper patient restraint and the use of a mouth speculum, bright light source, dental mirror or oral endoscope are required to fully inspect the equine oral cavity. Diastemata diagnosed early and managed properly can prevent the progression of periodontal disease and allow affected horses to preserve their dentition into old age.