The journal impact factor (IF), which is published annually by the Institute for Scientific Information, (Philadelphia, USA), is meanwhile in widespread use as a scientometric parameter for the evaluation of research and researchers in Germany and other European countries. The present article subjects the IF to critical analysis. It first deals with processes of production, transfer, and use of medical knowledge, because the IF intervenes in these processes on account of its reflexivity. Secondary effects of the IF resulting from its reflexivity are discussed with the focus on the level of the author, the journal and the medical discipline as well as on social knowledge processes in society. In addition, the extent to which the IF is appropriate for evaluating the quality of a specific article, of a journal or of individual and collective research achievements is discussed. The present article calls for (1) research evaluation in accordance with the recommendations of the Deutsche Forschungsgemeinschaft (German Research Council) and of the Arbeitsgemeinschaft der Wissenschaftlichen Medizinischen Fachgesellschaften (Association of the Scientific Medical Societies) and (2) more intensive occupation with and organization of medical knowledge processes.