Aim To demonstrate the need for proper restoration of root-filled teeth. Summary Tooth fracture can be a sequel to root-canal treatment, It is associated with the removal of excessive amounts of the tooth substance during the instrumentation phase, the use of unnecessary force during obturation, or inadequate planning of the design of the eventual coronal restoration to include appropriate cuspal protection Rarely, a fracture may be present in a tooth before treatment commences, but remains undetected. A case describing incomplete vertical tooth fracture of a root-filled mandibular first molar is presented, Key learning points Failure to provide a root-filled tooth with a restoration incorporating adequate cuspal protection can lead to subsequent tooth fracture, Large intracoronal restorations should be avoided when restoring root-filled teeth, particularly when marginal ridges have been lost.