In 1993, rectal swabs from clinically suspected cases of cholera admitted to the Infectious Diseases Hospital (IDH), Delhi were examined for Vibrio cholerae O1 and O139. Epidemiological data of 396 cholera cases were collected before the patients' discharge from IDH. Of the 1528 laboratory-confirmed cholera cases, 46% and 54% were caused by serotype O1 and O139 respectively. Both serotypes appeared and disappeared simultaneously, and peaked during the same time of the year. However, the two serotypes affected persons of different age groups; about 65% of the O1 cases occurred in children aged less than 10 years, whereas this age group accounted for 40% of the cases due to V. cholerae O139. Although there were some focal outbreaks due to serotype O139, both serotypes had almost similar geographical distributions. Important risk factors for transmission of cholera were almost equally prevalent in the majority of both types of cholera cases. Since the seasonality, geographical distribution, and risk factors for transmission were similar for both serotypes, the study indicates that the preventive and control measures are also likely to be similar. The study also shows that the emergence of V. cholerae O139 in 1993 did not affect the incidence, seasonality, and epidemiology of endemic V. cholerae O1 E1 Tor strains in Delhi.