Real, perceived and unknown adverse events secondary to vaccinations are a source of concern for care providers of children. In the USA large linked databases have provided helpful information regarding the safety of vaccines. Very little prospectively collected data on vaccine safety is available from resource poor countries, but safety concerns may be even more relevant in such settings. Vaccine manufacturers do not have to pass the same rigorous safety standards as vaccine manufacturers in rich countries. Vaccines, which protect against cholera, Japanese encephalitis, rabies or typhoid fever are predominantly used in resource poor, tropical countries and frequently do not undergo vigorous post marketing surveillance. New vaccines specifically suited for resource poor countries are sometimes marketed without the scrutiny of vigilant, independent regulatory authorities. We describe here the design and implementation of a large linked database for a semi-rural province in central Vietnam. The design overcomes several problems inherent in data bases of medical events and vaccinations in developing countries. Assigning a permanent identification (ID) number to each resident avoids the ambiguities of ID numbers based on the address. The distribution and use of medical identification cards with a permanent ID number assists in the unambiguous identification of vaccinees and patients. Medical records of all admissions are coded according to International Classification of Diseases (ICD-10) and transcribed into a computer system. Because these processes are novel the data collected by the study will be validated. Project staff will check records on vaccinations and hospital admissions through household visits at regular intervals. Data describing vaccinations and medical events are linked to the data collected by the project staff in a computer system. Based on the validation of the data we hope to optimize this model. Once we find the model working it is planned export this vaccine data safety link to other settings of similar economic status.