It is necessary to subject published research to critical scrutiny, in order to evaluate the robustness of the findings. The criteria used in evaluation require to be appropriate for the research paradigm, i.e. quantitative or qualitative. Quantitative conceptualizations of reliability and validity are unsuitable for evaluation of qualitative research as they were not devised for this purpose. The use of quantitative criteria to evaluate qualitative research may create the impression that the latter is not academically rigorous. Evaluation criteria which are specific to qualitative research require identification and application, in order to provide a formalized and rigorous approach to critical appraisal. A formalized framework for evaluation will help to ensure that the contribution of qualitative studies, with specific reference to health services research, receives optimum recognition. The work of a number of writers is used in this paper to examine the features which distinguish qualitative research and the following are discussed: the need for researcher reflexivity; the use of the 'first person' in academic work; the context in which research takes place; the selection of research participants; the interpretation of participants' accounts; the active acknowledgement of 'lay' knowledge; researcher flexibility within the research process; the generalizability of findings. It is concluded that academically rigorous criteria, which are appropriate for evaluation of qualitative research, exist and are available for use by practitioners and researchers.