Diphtheria is an acute infectious disease of upper respiratory tract caused by toxigenic strains of Corynebacterium diphtheriae (CD) and Corynebacterium other than diphtheria (COD). The organism is locally invasive and causes exotoxin - mediated illness and can lead to complications like stridor, respiratory obstruction, myocarditis, nerve palsy, renal insufficiency and death in severe cases. The objective of The study was to isolate, identify and confirm the organisms in the laboratory from the throat swabs of clinical diphtheria cases, correlate clinical disease and immunization status of the individual and compare serum antibody titers in immunized & non immunized patients with clinical disease. One hundred fifty patients presenting with fever, sore throat and membrane in the throat were included in the study and throat swabs were collected for direct microscopic examination for KLB and culture. In vitro Toxigenicity, testing by Elek’s Gel precipitation test was done for all CD isolates. Serum samples were tested for circulating anti diphtheria IgG antibody levels by ELISA. Results Showed Out of one hundred fifty clinical cases, fifty were culture positive of which thirteen were both culture and KLB positive. Elek’s gel precipitation test was positive for two CD positive cases. ELISA showed the rise in antibody titer in twenty-two patients. CD was isolated in six immunized and ten non immunized individuals COD was isolated in fourteen immunized and twenty non immunized individuals.The present study concludes that diphtheria due to CD is severe and associated with high morbidity and mortality. It affects non immunized and those with low protective circulating IgG antibodies. The disease can occur in milder form in immunized individuals.