Fatigue is regarded as a universal and unavoidable side effect of cancer therapy, yet its epidemiology and prevalence in populations of people with cancer have not been well-documented. Using the conceptual framework of Piper, et al., this study examined and described the perception and manifestations of fatigue and its physiological, biochemical, and behavioral correlates. A convenience sample (N = 77) of people with lung (n = 33) or breast cancer (n = 44) completed several instruments: a brief questionnaire, the Rhoten Fatigue Scale, a visual analogue scale (VAS), the Rhoten Fatigue Checklist, and the shortened version of the Profile of Mood States (POMS). Data on other factors thought to influence fatigue were collected via medical record audit. Seventy-five of 76 people (99%) completing the VAS experienced some level of fatigue. Significant correlates of fatigue included level of pain and POMS scores. Preliminary findings suggest that fatigue is a common problem with a complex etiology and that nurses must consider potential contributing factors when assessing fatigue and its impact on the individual.