Abstract : Leprosy is a chronic granulomatous condition caused by Mycobacterium leprae. Its diagnosis involves clinical evaluation supported by bacteriological, serological, and histopathological examinations. Measurement of IgM antibodies against phenolic glycolipid-1 (PGL-1) may assist in patient assessment of disease activity. Four cases with varying clinical types were documented: one lepromatous leprosy (LL), one tuberculoid tuberculoid (TT), and two borderline tuberculoid (BT) cases. Two patients showed concordant positive or high serological and bacteriological results. One patient demonstrated negative results for both tests, whereas one showed positive serology despite a negative acid-fast bacillus (AFB) smear. Discrepancies between serology and histopathology were observed primarily in borderline cases. Anti-PGL-1 IgM levels reflect the humoral immune response to M. leprae antigens but do not always correlate directly with the microscopic bacterial load. Antibody titers may remain elevated even when bacilli are inactive, suggesting antigen persistence or residual immunologic activity. Discordance between serologic and histopathologic findings in borderline patients reflects the dynamic nature of immunity and tissue morphology, which may not progress in parallel with clinical status. Anti-PGL-1 IgM testing serves as an important adjunct for diagnosis and therapeutic monitoring in leprosy, especially in patients with negative AFB smears. Integrating clinical, serological, bacteriological, and histopathological assessments can enhance the accuracy of PB–MB classification and support treatment decisions.