Background & objectives: Extended spectrum [beta]-1actamases (ESBLs) have emerged as a major threat worldwide with limited treatment options. The genotypes of ESBL producing strains largely remain unknown in India; hence the present study was aimed to determine the occurrence of ESBLs in Escherichia coli and Klebsiella pneumoniae, their molecular types and associated risk factors in a tertiary care hospital. Methods: Total 200 consecutive clinical isolates of E. coli (n=143) and K. pneumoniae (n=57) collected between February and July 2006 at Sanjay Gandhi Postgraduate Institute of Medical Sciences, a tertiary care hospital in north India, were examined phenotypically for ESBL production. ESBL strains were further typed for the [bla.sub.TEM/SHV/CTX-M] genes by PCR using specific primers. The [bla.sub.CTX-M] cluster was identified by restriction analysis and genotype by sequencing of PCR product. Resistance tn other antimicrobial agents was also studied. Various risk factors associated with ESBL infections were analyzed by logistic regressions.