Analyzing many year's data on the prevalence of giardiasis among Volgograd dwellers indicated that the five-year infectivity index did not substantially change and it was 6.3 +/- 0.4%. The rate of Giardia lamblia isolation was higher in healthy individuals in the high-loaded environmental topodemic regions of the city than in those in the good ones. Over 50% of all the cases of giardiasis were recorded among 7-15-year-old children, the proportion of preschool children was much less (31.9%). The rate of giardiasis detection in children who went to children's preschool facilities was twice higher than that in the unorganized population. The focality index was 6.8%, which is indicative of the low contagiousness of the disease.