The purpose of this cross-sectional correlational study was to examine the effects of patient and nursing unit characteristics on nursing-sensitive patient outcomes. The conceptual framework for this study is generated from the Quality Health Outcomes Model. The patient characteristics were patient age, gender, education, duration of illness, severity of illness, and illness representation. The nursing unit characteristics were nurse experience, nurse staffing, nursing unit competency, and group cohesion. Nursing-sensitive patient outcomes were patient’s confidence in self-care and patient’s perception of being well-cared for. Stratified sampling was employed to recruit a sample of 130 hospitalized chronically ill patients in 8 medical care units of 4 hospitals in Thailand. A face-to-face questionnaire interview was used to collect data from patients. A self-administered questionnaire was used to collect data from 90. Nurse staffing data were obtained from nursing administrative data for each unit. Multiple regression analyses were used to examine the relationships, test a mediator, and analyze the contextual effect of the study variables. Severity of illness (β = -.315, p <.01) and illness representation (β = -.234, p < .05) were significant predictors of patient’s confidence in self-care, when controlling for nursing unit characteristics. Illness representation partially mediated the relationship between severity of illness and patient’s confidence in self-care. Nursing unit characteristics were not significant predictors of patient’s confidence in self-care, when controlling for patient characteristics. There was a significant individual effect on patient’s confidence in self-care. Severity of illness (r = -.199, p < .05) and group cohesion (r = -.195, p < .05) were correlated with patient’s perception of being well-cared for. The findings of this study reinforce the need for acute care nurses to be aware of how chronically ill patients perceive health threats since illness representation directly affects patient’s confidence in self-care. Through understanding the role of illness representation as a mediator between severity of illness and confidence in self-care, it is suggested that nurses can improve patient’s confidence in self-care in severely ill patients by providing nursing interventions that promote positive illness representation.