Two infants with fibrosarcoma and rhabdomyosarcoma diagnosed prenatally and at 2 months of age, respectively, and cytomegalovirus (CMV) infection are reported. Concomitant CMV infection was revealed by positive urine culture and/or CMV DNA, and CMV-specific IgM, IgA, and complement-fixing antibodies. The patients, showing very low levels of immune T cells, died at 3 and 8 months of age, respectively. A pathogenic role for CMV in the progression of the tumors is suggested.