In this paper, we present the design, implementation and evaluation of FESMI, a fuzzy expert system that deals with diagnosis and treatment of male impotence. The diagnosis process, linguistic variables and their values were modeled based on expert’s knowledge the statistical analysis of the records of 70 patients from a hospital database and existing literature. The expert system has been implemented in FuzzyCLIPS. The fuzzy rules are organized in groups to be able to simulate the diagnosis process. Experimental results showed that FESMI did quite better than non-expert urologists and about 79% as well as the expert did.