Over the past two decades, numerous efforts have been initiated to improve screening and early detection of melanoma both in the United States and worldwide. It is commonly believed that these efforts have contributed to the stabilization of melanoma mortality, and that the proportion of thick melanoma with unfavorable prognosis is on the decline. Data obtained from 17 population-based cancer registries of the Surveillance Epidemiology and End Result (SEER) program of the National Cancer Institute for 1988-2006 were used to examine trends in melanoma tumor thickness. For malignant melanoma cases with recorded thickness, the proportionate distribution among four thickness categories (<or=1, 1.01-2, 2.01-4, and >4 mm) remained relatively stable over the 19-year study period, however, for melanomas resulting in death, the proportion of thick tumors increased. The most substantial change occurred in the proportion of melanoma in situ, which nearly doubled from 1988 to 2006. Surveillance and early detection efforts in the United States have not resulted in a substantial reduction in the proportion of tumors with prognostically unfavorable thickness. Continued improvement and new methods of screening, especially among demographics with higher incidence of thick tumors, is necessary.