SEN is a newly discovered blood-transmissible virus. Among its variants, SENV-D and -H are most often associated with non-A, -E hepatitis. Very little is known about the risk of vertical transmission of the virus. By using polymerase chain reaction with specific primers for SENV-D and -H, we investigated the prevalence of SENV-H and -D infection, the transmission rate of SENV infection and clinical features of SENV-infected children in 89 hepatitis C virus (HCV)-positive human immunodeficiency virus type 1-negative mothers. SENV infection was found in 36 (40%) mothers, and SENV-D was more frequent than SENV-H infection (34/36, 94%vs 5/36, 14%, P < 0.01). No difference in SENV infection rates was found between injection drug user (IDU) mothers (17/51, 33%) and mothers with no risk for bloodborne infection (19/38, 50%, P = ns). SENV-H infection was found only in IDU mothers and mothers with HCV genotype1b. Both SENV-D and -H can be transmitted to the offspring with an overall rate of 47%. Vertical transmission of HCV does not facilitate SENV infection of the offspring. Among 17 SENV-infected children, none was co-infected with HCV. Maternal HCV genotype or viral load does not interfere with mother-to-infant transmission of SENV. Persistence of SENV infection was demonstrated in 100% of infected children after 1-year follow-up, but none had clinical evidence of liver disease.