This chapter has been written to specifically address the usefulness of qualitative research for the practice of clinical epidemiology. The methods of grounded theory to facilitate understanding of human behavior and construction of monitoring scales for use in quantitative studies are discussed. In end-stage renal disease patients receiving long-term hemodialysis, a qualitative study used grounded theory to generate a multilayered classification system, which culminated in a substantive theory on living with end-stage renal disease and hemodialysis. The qualitative database was revisited for the purpose of scale development and led to the Patient Perception of Hemodialysis Scale (PPHS). The quantitative study confirmed that the PPHS was psychometrically valid and reliable and supported the major premises of the substantive theory.