Colonization factor antigens (CFAs) mediate attachment of enterotoxigenic Escherichia coli (ETEC) to the intestinal mucosa and induce protective immunity against ETEC diarrhea. ETEC strains (n = 111) isolated from North Indian children from 1985 to 1989 were examined for CFAs and putative colonization factors (PCFs). CFA/IV was the most common factor (26%), followed by coli surface antigen 17 (CS17) (19%), CFA/I (14%), PCFO166 (7%), and CFA/II (5%), while 24% of the isolates were negative for CFAs and PCFs. Among the strains producing heat-stable and heat-labile toxin (ST+LT+ strains), the STaI gene was strongly associated with the absence of known CFAs and PCFs, making the STaI+LT+ isolates an interesting target for the identification of previously undescribed factors. Repetitive sequence--based polymerase chain reaction revealed that the CS17+ strains, although clonally related, represented endemically circulating strains with a diversity greater than that of the CFA/I+ strains, which showed a substantial clonal clustering.