The objective of the present paper is to assess stigma and to create an abbreviated 12-item Stigma Scale based on the 40-item Berger's Stigma Scale for Thai youth living with HIV (TYLH). TYLH aged 16-25 years answered the 40-item Stigma Scale and the questionnaires on mental health, social support, quality of life and alcohol/substance use. Sixty-two (88.6%) of 70 TYLH reported at least one person knowing their serostatus. Men having sex with men were more likely to disclose the diagnosis to friends (43.9% versus 6.1%, P < 0.01) and less likely to disclose to families (47.6% versus 91.8%, P < 0.01). Women were more likely to disclose to families (90.2% versus 62.1%, P < 0.01) and less likely to disclose to friends (7.3% versus 31%, P < 0.05). The 12-item Stigma Scale was reliable (Cronbach's alpha, 0.75) and highly correlated with the 40-item scale (r = 0.846, P < 0.01). Half of TYLH had mental health problems. The 12-item Stigma Scale score was significantly associated with mental health problems (beta = 0.21, P < 0.05). Public attitudes towards HIV were associated with poorer quality of life (beta = -1.41, P < 0.01) and mental health problems (beta = 1.18, P < 0.01). In conclusion, the12-item Stigma Scale was reliable for TYLH. Increasing public understanding and education could reduce stigma and improve mental health and quality of life in TYLH.