Pontianak City is one of the areas in Indonesia which is prone and endemic to dengue fever. Since 2002 until the year 2013, dengue fever has become a remarkable incident in the city for several time. Determination of areas potentially vulnerable to dengue frver is usually done by the health service area of prevention and mitigation of disease, manually based on frequency of occurrence data of dangue fever that occurent in previous years. Therefore, this research aims to produce a system that can determine areas of potentially dengue fever with feature(indicator) that have the specified in the amount of precipitation, air temperature, air humidity, the number of health facilities, overcrowding and the frequency of occurrence of dengue. The system was builtin determining areas of potentially dengue fever using Case Base Reasoning (CBR). To Generate an output in the form of insecurity level status using the similarity value, the methot used is Simple Matching Coefficient Method. The output of this system is the status os insecurity, which is no dengue fever pround, prone and very prone.