This study discusses the impact of stress specific to being lesbian, gay, or bisexual (LGB)—measured by means of the concepts of stigma consciousness and internalized homonegativity—on the mental well-being of LGB youth. Also, the effects of positive and negative social support were considered within the model. The sample consisted of 743 LGBs less than 26 years old who were recruited during the online ZZZIP survey in Flanders, Belgium. Hierarchical regression shows that LGB-specific unsupportive social interactions have the greatest direct effect on mental well-being of LGB youth, followed respectively by stigma consciousness, internalized homonegativity, and confidant support.