We present a simple, formal, lexicon-based method for automated indexing of diagnoses based on the Systematized Nomenclature of Medicine (SNOMED II), called the LBI-method. Part 1 gives an introduction to the LBI-method and presents its realization as application system SALBIDH. The underlying model states that a diagnosis is represented by a set of indices of any nomenclature. The LBI-method is defined as a composition of functions, which in turn define the 3 steps of the LBI-method: preprocessing, morphological analysis, and semantic analysis. Part 2 will focus on the design and the results of an evaluation study to judge the quality of the LBI-method. In this evaluation study the quality of automated indexing was examined as well as the quality of the retrieval of patient data by using automated indexed diagnoses.