INH is the most potent anti–TB drug and is the main part of any first–line treatment regimen for TB. Loss of therapeutic efficacy of this important anti–TB drug has considerable implications for control strategies and potential for patients. The present study was designed to provide the clinical profile of patients with INH–monoresistance in Madurai district. This retrospective study was performed at the IRL attached to Madurai Medical College. The classical information i.e., age, gender, sputum sample grading and drug susceptibility testing (DST) patterns for each patient that was referred to IRL from January 2018 to December 2018 was retrospectively analyzed. The LPA was performed according to the manufacturer‘s protocol. During the study period, a total of 1317 clinical isolates of TB were collected from different parts of Madurai district, of which 227 samples were found to be INH monoresistant (17.2%). Most of these INH monoresistant patients were in the age group 46 to 55 yrs (33%) and 73% were males. An important challenge for TB control is the emergence of strains that are resistant to the most potent anti–TB agents i.e. INH