A case of Klinefelter's syndrome with the development of a mediastinal 
teratocarcinoma is reported suggesting that the association of a 
gonadotropin-secreting tumor with the XXY chromosomal abnormality may be more 
than coincidental. Whereas this child appeared to survive the effects of the 
teratocarcinoma, he succumbed to acute leukemia two years later. This prompted a 
review of secondary leukemias in children following chemotherapy/radiotherapy 
for another primary malignancy. These patients responded poorly to treatment of 
the secondary leukemia with a median survival of about four months. The 
incidence of secondary leukemias might be expected to be on the rise as 
increasing numbers of pediatric cancer patients are surviving longer after 
treatment with agents that are potentially leukemogenic or carcinogenic 
themselves. Children who have survived cancer and its therapy present special 
problems and it will be necessary for the pediatrician and practitioner to 
monitor these children.