Sera from 185 HBsAg carrier, pregnant Saudi women were tested for HBeAg, antibody to HBeAg (anti-HBe) and for antibody to hepatitis D virus (anti-HDV); 9.7% of the carrier mothers were anti-HDV-positive and the majority of them (94.4%) were anti-HBe-positive. Follow-up of 17 infants of anti-HDV-positive carrier mothers until about 7 months of age showed no evidence of perinatal transmission of HDV. Age-specific prevalence of anti-HDV in 280 Saudi carriers showed that infection with HDV is infrequent in infants and is mainly acquired during the second and third decades of life, which suggests that transmission of HDV is predominantly horizontal.