The question addressed in this study was: Can the critical defining characteristics (CDCs) of nursing diagnoses be determined by magnitude estimation scaling (MES)? MES was used by having 32 nurse subjects numerically estimate the magnitude of each characteristic of anxiety and of sleep pattern disturbance on each of three concept dimensions: importance, frequency, and competency. Geometric means of the stimuli for each of the concept dimensions were computed and correlated with each other. Strong correlations between the characteristics and the concept dimensions were obtained. It was concluded that MES is a useful technique for identifying the CDCs and operational definitions of nursing diagnoses.