Stigma regarding HIV pre-exposure prophylaxis (PrEP) is commonly implicated as a factor limiting the scale-up of this highly effective HIV prevention modality. To quantify and characterize PrEP stigma, we developed and validated a brief HIV PrEP Stigma Scale (HPSS) among a group of 279 men who have sex with men (MSM). Scale development was informed by a theoretical model to enhance content validity. We assessed two scale versions, Semantic Differential and Likert, randomizing the order in which scales were presented to participants. Both scales demonstrated high internal consistency. The Likert scale had substantially better construct validity and was selected as the preferred option. Scale scores demonstrated construct validity through association with constructs of interest: healthcare distrust, HIV knowledge, perceived proportion of friends/partners on PrEP, perceived community evaluation of PrEP, and perceived effectiveness of PrEP. The scale accounted for 25% of the total variance in reported willingness to be on PrEP, indicating the substantial role PrEP stigma may have on decisions to initiate PrEP. Given increased efforts to roll-out PrEP, having a valid tool to determine the level and types of PrEP stigma in individuals, groups, and communities can help direct implementation plans, identify goals for stigma reduction, and monitor progress over time.