PurposeAdolescent gay and bisexual men (AGBM) are disproportionately affected by human immunodeficiency virus (HIV), but little is known about testing rates among men aged 18 years and under or about the barriers that they face when contemplating an HIV test. Therefore, we investigate here the testing behaviors and barriers among a diverse national sample of AGBM. MethodsA total of 302 AGBM aged 14–18 years were recruited via Facebook ads to participate in an mHealth (text messaging-based) HIV prevention program. Recruitment was stratified to ensure approximately 50% were sexually inexperienced. ResultsOnly 30% of sexually active participants had ever been tested for HIV, and nearly half of them did not know where they could go to get tested for HIV (42.9%). Based on exploratory factor analysis, nine questions assessing potential barriers to HIV testing factored into three subscales: external factors, fear, and feelings of invincibility. Among sexually active participants, those who had never tested for HIV had significantly greater scores on the external factors (odds ratio, 1.63; 95% confidence interval, 1.01–2.66) and fear (odds ratio, 1.88; 95% confidence interval, 1.11–3.19) subscale. Older (16–18 years old) youth were especially likely to be affected by external factor barriers, and fear was associated with never testing among gay-identified individuals. ConclusionsHIV testing rates were low among AGBM. Several modifiable barriers emerged, especially a lack of knowledge about the closest testing site. Interventions and programs that target high school–age adolescents could address external barriers by introducing HIV testing services into high schools.