Self-efficacy has been shown to influence student performance by affecting behaviors that are linked to increased academic success. This study examines self-efficacy in a nursing context, specifically with regard to tasks needed to care for the critically ill patient. The literature review argues that nurses' self-efficacy for their ability to perform patient care affects their performance of nursing tasks. In the current healthcare climate, where great emphasis has been placed on decreasing patient errors and risk, student nurses who have self-doubts about their ability may not even initiate a nursing care task in order to avoid making a mistake. The focus of this study was development and refinement of a psychometrically sound instrument to measure nursing students' perceived self-efficacy for performance of patient care tasks. Item Response Theory was used to accomplish this goal, as current measurement of self-efficacy is typically done using classical true score theory, which has inherent limitations with regard to score interpretation. Item response theory is an improved measurement model that provides more detailed information about test or survey items and those who respond to them. After item development and pilot testing, the Nursing Student Self-Efficacy Scale (NSSES) was administered to 256 nursing students at large public university and 149 nursing students at a local community college. Analysis of information obtained for items from the self-efficacy for psychomotor skills, communication, and knowledge subscales provided evidence for reliable interpretation of scores indicating self-efficacy beliefs. Comparison of estimated self-efficacy from students at different levels of the nursing program provided validity evidence in that the NSESS could discriminate between beginning students and more advanced students who possessed different levels of self-efficacy for skills due to their level of program completion.