Although there is still much to learn about the types of errors committed in health care and why they occur, enough is known today to recognize that a serious concern exists for patients. Tuberculosis (TB) is an infectious disease that is frequently subject to diagnostic errors. Missed or delayed diagnosis of TB can affect patients and community adversely. Our aim in the present study was at evaluating the type of diagnostic errors in TB patients from symptom onset to diagnosis. This was a multicenter cross-sectional study conducted in three university hospitals in Mashhad, Iran. We showed a long delay in diagnosing TB that is mostly related to the time from first medical visit to diagnosis. Errors in the diagnostic process were identified in 97.5% of patients. The most common type of error in diagnosing TB was failure in hypothesis generation (72%), followed by history taking and physical examination. In conclusion, it seems likely that efforts to improve public awareness of and health literacy for TB, to coordinate the referral and follow-up systems of patients, and to improve physicians' skills in history taking and physical examination and clinical reasoning will result in reduced delay in diagnosis of TB and, perhaps, improved patient safety and community health.