Between 1996 and 1998, 1064 cases of giardiosis were reported in Norway, with less than 25% attributed to infection acquired within the country. Between 1999 and 2002, 1547 cases of giardiosis were reported (mean of 386 cases per year; 8.5 cases per 100.000 population). The rise in of infection is attributed to increased immigration and foreign travel (Folkehelseinstituttet, large proportion of diarrhoeal illnesses is attributed to an unknown cause. The type of risk assessment presented here can assist in focussing research and surveillance to decrease the knowledge gap.