There is an ongoing debate regarding the nature of narcissism such that some argue that narcissistic individuals oscillate between grandiose and vulnerable states, whereas others argue these dimensions are stable traits (e.g., grandiose individuals remain in grandiose states). Scales sensitive to fluctuations in narcissistic states are necessary to address this question. The current study (N = 1,613 across three samples) validates the newly developed Narcissistic Vulnerability Scale (NVS), a brief (11-item) adjective-based measure of vulnerable narcissism. Expert ratings were used for item selection. The NVS’s factor structure was evaluated along with its correlations with measures of grandiose and vulnerable narcissism, five-factor model traits, and self-esteem. A subset of NVS items were also evaluated using an ecological momentary assessment design. Results indicate the NVS is a unidimensional measure of vulnerable narcissism that could be used in either trait-oriented or state-oriented analyses, the latter of which may be particularly well suited to answering the most pressing questions in the study of narcissism.