In 2004, suicide was the third leading cause of death among youths and young adults aged 10-24 years in the United States, accounting for 4,599 deaths. During 1990-2003, the combined suicide rate for persons aged 10-24 years declined 28.5%, from 9.48 to 6.78 per 100,000 persons. However, from 2003 to 2004, the rate increased by 8.0%, from 6.78 to 7.32, the largest single-year increase during 1990-2004. To characterize U.S. trends in suicide among persons aged 10-24 years, CDC analyzed data recorded during 1990-2004, the most recent data available. Results of that analysis indicated that, from 2003 to 2004, suicide rates for three sex-age groups (i.e., females aged 10-14 years and 15-19 years and males aged 15-19 years) departed upward significantly from otherwise declining trends. Results further indicated that suicides both by hanging/suffocation and poisoning among females aged 10-14 years and 15-19 years increased from 2003 to 2004 and were significantly in excess of trends in both groups. The results suggest that increases in suicide and changes in suicidal behavior might have occurred among youths in certain sex-age groups, especially females aged 10-19 years. Closer examination of these trends is warranted at federal and state levels. Where indicated, health authorities and program directors should consider focusing suicide-prevention activities on these groups to help prevent suicide rates from increasing further.