From January 1962 to July 1988, 34 infants less than 29 days of age who had cancer were seen at St. Jude Children's Research Hospital (SJCRH). The malignancies in this group consisted of 19 neuroblastomas, 6 leukemias, 3 retinoblastomas, 2 Wilms' tumors, 2 melanomas, and 2 teratomas. Twenty-three patients (68%) are alive and free of disease 2 months to 24 years after diagnosis. We reviewed the presentation and initial symptoms, pathology reports, patient population, associated anomalies, potential genetic influences, and possible perinatal factors. The most common initial symptom was an enlarging abdomen or abdominal mass. Pathological findings were occasionally difficult to interpret; five additional infants who were referred to us did not have malignancies. There was no increased incidence of associated anomalies or perinatal insults. The only genetic factor was retinoblastoma in one parent of each infant diagnosed as having retinoblastoma. The possible etiology of neonatal tumors is discussed.