During the period from March through November 1989, 70 children who were attended at the Pediatric Department at Central Hospital in Valencia, were enrolled in the study, it was thought that Giardia lamblia infection might be present. Giardia L. were identified using two different diagnostic procedures: from stool samples and duodenal aspirates for cysts or trophozoites examination. These children were treated with Metronidazole three dosage of 15, 30 and 50 mg/kg per day for a ten day period. Our study showed predominant giardiasis in children with ages ranging from 2 to 6 years old (60%) with a relationship between female and male sex 1.05:1. In this series, 72.8% of patients presented normal nutrition, and 55.7% of them were from the suburban area. The most frequent symptoms were abdominal pain, diarrhea, vomiting, abdominal distention, constipation and flatulence. The infants prevalent symptom was diarrhea (83.3%) and the older children and school children prevalent symptom was abdominal pain with 78.5 and 100% respectively. In this study, stool examination was positive in 97.1% of the children and duodenal aspirate was positive in all 70 children (100%); the first procedure showed predominant Giardia cysts (88.2%) and the second one showed predominant trophozoites (47.1%). All 70 patients (100%) were cured with Metronidazole to different dosage. Side effects were seen with only the maxim dose, such as nausea 40%, headache 10% and appearance of yeast into 50% of duodenal aspirate.