Summary. Earlier studies addressing the hepatitis B virus (HBV) DNA cut-off level for inactive chronic HBV infection largely involved patients with normal alanine aminotransferase (ALT) for only 1–2 years and based on a single time HBV DNA assay. This study was conducted to address this issue using serial HBV DNA assays in patients with persistently normal ALT (PNALT) over 10 years following spontaneous hepatitis B e antigen (HBeAg) seroconversion. Serial serum specimens (mean 9 samples per patient) of 62 patients with PNALT and no disease progression over 10 years (median 18.1 years) after spontaneous HBeAg seroconversion were assayed for HBV DNA. Excluding assays within 1 year after HBeAg seroconversion, 21% and 82.3% of the patients with PNALT had HBV DNA levels persistently lower than 4 log10 and 5 log10 copies/mL, respectively, and only 8% had a level ≥5 log10 copies/mL in at least two assays. Of the 27 patients with PNALT defined by ALT <30 U/L for male and <19 U/L for female, only 33% had serum HBV DNA level persistently <4 log10 copies/mL. There was no significant difference in the serial HBV DNA changes among patients with different gender, HBV genotype or age at HBeAg seroconversion. Liver biopsy in nine patients invariably showed minimal necroinflammation and one showed Ishak fibrosis score 4. These results suggest that 5 log10 copies/mL (20 000 IU/mL) is a more appropriate cut-off HBV DNA level for inactive chronic HBV infection in the setting of PNALT.