BACKGROUND: In high tuberculosis (TB) burden, r esource-poor countries, sputum smear microscopy remains the mainstay of diagnosis. The low sensitivity of this test means that patients with smear-negative but culture-positive TB pass undetected through the health care system. Such clinical episodes are missed opportunities for diagnosis and interruption of transmission, which might be averted through the application of more sensitive diagnostic tests. OBJECTIVES: To estimate the proportion of incident TB cases that might have been detected earlier than the actual date of diagnosis if a test more sensitive than smear microscopy had been used at an earlier presentation episode. METHOD: Retrospective cohort study in urban Peru, investigating health care facility interactions for symptoms suggestive of TB prior to TB diagnosis through patient interviews and a review of clinical records. RESULTS: Of 212 participants enrolled, 58% had one or more clinical interactions prior to their diagnostic episode. Of those with a prior episode, the median number of episodes was three. The median delay to diagnosis from first presentation was 26 days. CONCLUSION: There are clear missed opportunities for earlier TB diagnosis, delaying treatment initiation and continued spread of Mycobacterium tuberculosis to the community. The implementation of sensitive diagnostic tests appropriate to resource-poor settings should be given high priority.