It is a preliminary study testing the applicability of a method for knowledge characterization based on graphs theory. 11 (eleven) nurses working in a medical surgical intensive care unit including neurological patients constructed graphs to explain the diagnostic process. The results show that: the knowledge structure is in a developing stage; there is agreement regarding to diagnosis formulation and the data base on which it is founded is diversified and link to a specified form of related causes. The method demonstrated to be feasible and should be reapplied on a larger population.