CONTEXT: The Patient Care Monitor (PCM), version 2.0, is an electronic patient-reported outcomes instrument designed to be embedded into oncology practices. One key psychometric component of an instrument is its factor structure. OBJECTIVES: To validate the factor structure of the PCM. METHODS: The PCM was administered within various oncology clinics at our institution from 2006 to 2011 as part of standard of care, yielding a large (n = 5624) and diverse data set. An exploratory factor analysis was performed. RESULTS: The PCM performed well in terms of missing values and floor and ceiling effects. The three scales postulated by the PCM developers exhibited high internal consistency (Cronbach alpha 0.94-0.95); the six subscales exhibited good internal consistency (Cronbach alpha 0.80-0.95). A three-factor model approximated simple structure and was consistent with the constructs of emotional function, physical function, and physical symptoms suggested by the PCM developers. However, a six-factor model did not support the division of these three constructs into subscales of despair, distress, ambulation, impaired performance, treatment side effects, and general physical symptoms. Instead, we observed an emotional factor, a physical functioning factor, a factor including many of the treatment side effects, and three factors consisting of various clusters of physical symptoms. CONCLUSION: Although six subscales postulated by its developers perform reasonably, allocation of the PCM items to three constructs is more accurate and likely more consistent with how symptoms and concerns are conceptualized by patients.