This article describes the development and testing of a quantitative measure of HIV/AIDS stigma as experienced by people living with HIV/AIDS. This instrument is designed to measure perceived stigma, create a baseline from which to measure changes in stigma over time, and track potential progress towards reducing stigma. It was developed in three phases from 2003-2006: generating items based on results of focus group discussions; pilot testing and reducing the original list of items; and validating the instrument. Data for all phases were collected from five African countries: Lesotho, Malawi, South Africa, Swaziland and Tanzania. The instrument was validated with a sample of 1,477 persons living with HIV/AIDS from all of the five countries. The sample had a mean age of 36.1 years and 74.1% was female. The participants reported they knew they were HIV positive for an average of 3.4 years and 46% of the sample was taking antiretroviral medications. A six factor solution with 33 items explained 60.72% of the variance. Scale alpha reliabilities were examined and items that did not contribute to scale reliability were dropped. The factors included: Verbal Abuse (8 items, alpha=0.886); Negative Self-Perception (5 items, alpha=0.906); Health Care Neglect (7 items, alpha=0.832); Social Isolation (5 items, alpha=0.890); Fear of Contagion (6 items, alpha=0.795); and Workplace Stigma (2 items, alpha=0.758). This article reports on the development and validation of a new measure of stigma, HIV/AIDS Stigma Instrument - PLWA (HASI-P) providing evidence that supports adequate content and construct validity, modest concurrent validity, and acceptable internal consistency reliability for each of the six subscales and total score. The scale is available is several African languages.