Among patients with lung cancer, stigma is associated with negative psychosocial and behavioral outcomes. There is a need to develop psychometrically robust patient-reported outcome measures for stigma that incorporate perspectives of patients diagnosed with lung cancer. As part of our multiphase process of measure development and validation, we report on scale formation and preliminary psychometric evaluation of the Lung Cancer Stigma Inventory (LCSI). Building on previously reported concept elicitation (Phase I) work, Phase II of LCSI development involved item generation and refinement, informed by literature review, provider input, and patient (N = 20) feedback. Phase III focused on initial psychometric scale evaluation in a unique sample of 231 lung cancer patients. Based on provider input and patient cognitive interviews, 49 items were included in a preliminary measure. In an exploratory factor analysis of the 37 retained items, 3 factors emerged: perceived stigma, internalized stigma, and constrained disclosure. Internal consistency of the final, 25-item LCSI scale was high (Cronbach’s α = .89), and the 3 subscales demonstrated good internal consistency. The test–retest correlation was high (r = .91), suggesting strong stability of measurement over time. There was good convergent validity between the LCSI and an existing measure of lung cancer stigma, the Cataldo Lung Cancer Stigma Scale (r = .58, p < .001). In a multiphase process, we have developed a reliable, multidimensional measure of lung cancer stigma, the LCSI. Subsequent work will be conducted to establish further evidence of validity and clinically meaningful change.