Diagnosis is arguably the most critical component of all dental treatment, and Endodontics is no exception. Stedman’s medical dictionary describes clinical diagnosis as ‘‘the determination of the nature of a disease made from a study of the signs and symptoms of a disease.” The diagnostic process, therefore, is an essential part of treatment as well as treatment planning. Collection of information, history, signs and symptoms, a thorough clinical examination, and objective testing are mandatory prior to recommend and initiating treatment. Only after collecting this information can one come up with a diagnosis that benefits the patient. Providing the wrong treatment for a patient could not only intensify a patient’s symptom but make it even more difficult to arrive at the correct diagnosis. Knowledge of endodontic disease, radiographic interpretation, and clinical manifestations is an integral and important part of achieving the correct diagnosis.