From 1972 to 2000, 123 patients with solid tumors whose complaints had started in the first 28 days of life were retrospectively evaluated. Fifty-five patients were diagnosed in the first 28 days and 68 patients were diagnosed after 28 days. In the former group, 85.5% of patients had symptoms in the first day of life. In the latter group, 77.9% had the onset of symptoms in the first day. Tumor subgroups in the neonatal period included teratoma (34), neuroblastoma (11), rhabdomyosarcoma (3), Wilms tumor (1), and retinoblastoma (3), and the others (3). Three patients had other, less common tumors. In the second group the numbers were the following: for teratoma (32), neuroblastoma (15), germ cell tumors other than teratomas (8), rhabdomyosarcomas (4), the other soft tissue sarcomas (3), Wilms tumor (1), retinoblastoma (1), and other, rare tumors (4). There were 22 malignant tumors in the first group, and 44 in the second group. Fourteen patients in the first group died in the early postoperative period or with progressive disease. Nineteen of 44 patients died in the second group. Overall survival rates were 24.9% and 51.6% in first and second groups, respectively (p = 0.015). Event-free survival rates were 14.7% and 47.7% in these groups, respectively (p = 0.0063). This is the first report comparing clinical features and prognosis of tumors diagnosed in the first 28 days of the life with those diagnosed after 28 days. The prognosis was worse in infants diagnosed in the first 28 days of life.