A total of 431 rectal swabs, collected from acute diarrheal cases at a surveillance site and at different diarrheal outbreak areas of Orissa from May to October 2005, were bacteriologically analyzed. Out of 265 culture-positive samples, Vibrio cholerae O1 was isolated in 56 samples (20.8%), of which 37 were the Inaba serotype and 19 were the Ogawa. The antibiogram profile revealed that all the V. cholerae O1 Ogawa and Inaba serotypes were uniformly sensitive to ampicillin, chloramphenicol, gentamicin, ciprofloxacin, norfloxacin and tetracycline. The V. cholerae O1 Inaba serotypes were resistant to furazolidone and nalidixic acid, while the Ogawa strains were resistant to furazolidone, nalidixic acid and neomycin. The multiplex polymerase chain reaction (PCR) assay on some selected strains of both serotypes revealed that all the strains were positive for ctxA and tcpA genes showing biotype El Tor. The present study revealed the emergence of V. cholerae O1 biotype El Tor serotype Inaba, which caused sporadic outbreaks of cholera in 2005. The outbreaks of diarrheal disorders in one geographical area of the state (in the Pattamundai area, Kendrapara district) in 2005 were due to V. cholerae O1 Ogawa, whereas the other outbreaks in other areas (Puri, Khurda and Dhenkanal districts) from August to October 2005 were due to V. cholerae O1 serotype Inaba. This is the first report that an emergence of V. cholerae O1 serotype Inaba caused sporadic outbreaks of cholera in different parts of Orissa. Switching over of V. cholerae O1 Ogawa strains to Inaba, causing diarrheal outbreaks in Orissa, needs close monitoring.