The present integral clinical and laboratory study was carried out in 325 children infected with Hymenolepis nana. Results showed that H. nana is found among the top five intestinal parasitosis in school children in Mexico City, in the majority of the cases associated with protozoans and other helminths, especially and with Giardia lamblia. Although the amount of parasites found is small, the clinical manifestations vary very little with larger amounts. The most important and more constant clinical manifestations in those solely infected with H. nana and with other combinations are: abdominal pain, hyporexia and irritability. We have seen that in patients infected solely with H. nana, there is weight loss, meteorism and flatulences. In those associated with G. lamblia, diarrhea is one of the most frequent manifestations. Hymenolepiasis is an important disease in our environment due to its high frequency among pre-school and school children and its constant identifiable clinical manifestations.