Escherichia coli (E.coli) is a normal inhabitant of the human gastrointestinal tract able to cause a range of infections in the human host. It is the organism most frequently responsible for urinary tract infections that occur in the community and it is the bacterium most often causing diarrhoea in people travelling overseas. In recent years a strain called E.coli O157 has gained notoriety for causing foodborne infection which can have severe health consequences. This article describes the range of different infections caused by E.coli in primary care settings and clarifies the characteristics of the different strains of the bacteria that explain variations in their pathogenicity.