Hematologic investigations for 7 years at the Pediatric Department of Yonsei Medical Center of 52 syphilitic infants were reviewed. A moderate degree of anemia with red cell regeneration was observed in 40 infants (76.0%). Marked thrombocytopenia but without active bleeding was found in 19 infants, and with active bleeding in 3 infants. A wide range of leukocyte counts, relative lymphocytosis and monocytosis were prominant features. The jaundice was mainly due to unconjugated bilirubin in 6 infants, conjugated as well as unconjugated bilirubin in 8 infants. With therapy, the above abnormal hematologic findings showed marked improvement. Early diagnosis is essential. Prevention and congenital syphilis depend on a high level of clinical suspicion, supported by routine and diagnostic use of laboratory and serologic aids, in the asymptomatic or minimally symptomtaic infants.