OBJECTIVE This study investigated the viremia profiles in children with chronic hepatitis B virus (HBV) infection and spontaneous hepatitis B e antigen (HBeAg) seroconversion. METHODS Fifty-eight children with chronic HBV infection met the following criteria: normal alanine aminotransferase (ALT) level at enrollment, followed up for more than 10 years, no antiviral treatment, and having undergone spontaneous HBeAg seroconversion during follow-up evaluation. They were grouped according to the post-HBeAg seroconversion HBV-DNA levels: (1) low viremia: transient or never 10(4) copies/mL or greater (n=35) (2) fluctuating high viremia: 10(4) copies/mL or greater at least twice at intervals more than 1 year apart (n=23). Abdominal sonography, ALT, and HBV-DNA levels were assessed annually. Another 14 nonseroconverted children served as controls. The precore mutant (nt1896) and genotypes were examined. RESULTS The initial HBV-DNA level of the 58 seroconverters was 10(8.4+/-1.0) copies/mL and decreased to 10(2.9+/-2.0) copies/mL at the end of follow-up period. Their mean ages at enrollment, at peak HBV-DNA, at peak ALT, at HBeAg seroconversion, and at final follow-up were 7.0 +/- 3.7, 13.4 +/- 5.8, 16.3 +/- 6.0, 17.2 +/- 5.8, and 23.7 +/- 4.1 years, respectively. The precore mutant appeared more often in the fluctuating-high-viremia group than in the low-viremia group (60.9% vs 22.9%, P=.004). HBV genotypes had no effect on the viremia profiles. After HBeAg seroconversion, none had persistent abnormal ALT levels. CONCLUSIONS Generally, these young seroconverters had decreased viral loads, normal ALT levels, and uneventful courses after HBeAg seroconversion. A longer follow-up period is necessary to elucidate the significance of HBeAg seroconversion occurring in childhood and young adulthood.