In 2008, an increase in syphilis among young black men was noted in New York City (NYC), Miami-Fort Lauderdale, and Philadelphia. To explore this trend, we examined infectious syphilis cases from 2000 to 2008 among adolescent and young adult men in these areas.Descriptive analysis of male infectious syphilis cases reported to public health authorities in NYC, FL, and Philadelphia.From 2000 to 2008, infectious syphilis cases among males increased in NYC (107-1027 cases), Miami-Fort Lauderdale (109-374), and Philadelphia (41-142). This increase was largely attributable to cases among men who have sex with men. Rates among black adolescent males (15-19 years) increased in NYC ([2.6-43.0]/100,000), Miami-Fort Lauderdale ([5.5-48.1]/100,000), and Philadelphia (]8.3-40.3]/100,000). Among males with infectious syphilis in 2008 in NYC, 9.1% of blacks and 6.6% of Hispanics were adolescents compared with 1.6% of whites (P < 0.001). In Miami-Fort Lauderdale, 12.2% of black males were adolescents compared to 2.0% of whites (P < 0.01) and 2.7% of Hispanics (P < 0.01). Black males dominated all age groups in Philadelphia, but were more likely to be <25 years of age than whites (P = 0.02). Human immunodeficiency virus coinfection rates were 14.8% among adolescent males in NYC, 15.4% in Philadelphia, and 25.0% in Miami-Fort Lauderdale.Very young black males have emerged as a risk group for syphilis in these 3 areas, as have young Hispanic males in NYC. Many are men who have sex with men and some are already human immunodeficiency virus-infected. Targeted risk reduction interventions for these populations are critical.