In 2004-2005, the school deworming program in Vietnam targeted 2,400,000 school-children in 25 provinces. A questionnaire survey of a random sample of schools throughout the country was organized to validate the teacher feedback, assess the real coverage of the program and estimate the occurrence of side-effects. A total of 91 schools in four different provinces were visited few days after drug distribution. A total of 2,323 children and 80 teachers were questioned. The total cost of the monitoring has been estimated at US dollar 7,000 (less than 10% of the deworming program). The survey demonstrated a coverage of 95% for school-children and of 86.3% for teachers (on average a coverage 2% lower than the one reported by the teachers through forms on the day of drug administration). Approximately 0.4% of those interviewed reported side-effects after deworming, while the occurrence of side effects through routine reports was 0.15%. In both cases, the side effects were described as mild forms of nausea, abdominal pain, or headaches that did no required pharmacological treatment. The survey confirmed the positive results of routine reporting; we consider the survey a cost-effective activity to maintain the control activities under monitoring.