In this paper, we describe an intelligent system, combining Expert System and Case Based Reasoning tools, to assist clinicians in the diagnosis of Adverse Drug Reactions(ADRs). The expert system is used in the analysis phase, while case based reasoning is used to compare the proposed case to existing proved ADR cases. The imprecise and uncertain nature of the information associated with ADRs is handled by the use of generalized modus ponens. The system. Sirnulates the methodologies used by experts and is particularly well adapted not only to the rapid changes which characterize the domain of study but also to the uncertainty associated with the introduction of a new ADR.