As an introduction to a study day devoted to informatic in surgery, some basis knowledges are summarized: architecture and function of computers, programmation language, data bases. They are illustrated by various applications made in the "Cliniques St Luc" te Brussel namely patient monitoring, artificial pancreas, office system and operating room management system. The future use of local area network is proposed in order to achieve medical department independence and the needed cooperation between all users of medical and hospital informatic.