This case series describes observations of 12 patients who developed horizontal root fractures in non-endodontically treated teeth. Using clinical and radiographic examination, horizontal fractures were observed in eight maxillary first molars, one maxillary second molar, one mandibular first premolar and four mandibular second premolars. A total of 12 teeth had clinically intact crowns and 2 had carious. Eight fractures of maxillary molars occurred in the palatal roots, while one fracture was observed in the distobuccal root. Eleven patients experienced pain from the affected teeth during mastication. Within the limits of this case series, it was concluded that these fractures were related to; root morphology, damaging masticatory habits and excessive occlusal forces.