The Centers for Disease Control and Prevention recommends routine HIV screening in health care settings. Using national surveillance data, we assessed trends in HIV diagnoses and testing frequency in youth aged 13-24 diagnosed with HIV in 2005-2008. Diagnosis rates increased among black (17.0% per year), Hispanic (13.5%), and white males (8.8%), with increases driven by men who have sex with men (MSM). A higher percentage of white males and MSM had previously been tested than their counterparts. No increases in diagnoses or differences in testing were observed among females. Intensified interventions are needed to reduce HIV infections and racial/ethnic disparities.