We examined tuberculosis skin conversion rates for U.S. Navy and Marine Corps personnel for 1999 to 2002, using information submitted to the Navy Environmental Health Center (Portsmouth, Virginia). The screening of 1,190,866 Navy and Marine Corps personnel with tuberculosis skin testing found 17,439 (1.46%) new reactors. The annual conversion rate increased from 1.35% in 1999 to 1.33% in 2000, 1.54% in 2001, and 1.61% in 2003 [chi2 for trend (df = 1) = 102.368; p = 0.000]. The overall conversion rate for aircraft carriers was 0.52%, with significantly higher rates for amphibious ships (1.76%; relative risk, 3.33; 95% confidence interval, 2.98-3.71; p = 0.000) and Marine units (1.13%; relative risk, 2.17; 95% confidence interval, 1.98-2.38; p = 0.000). Annual conversion rates increased significantly over the period for aircraft carriers [chi2 for trend (df = 1) = 4.950; p = 0.02608] and decreased significantly for amphibious ships [chi2 for trend (df = 1) = 40.197; p = 0.000]. Conversion rates were consistent with the recent historical values for the Navy and Marine Corps.