Klinefelter syndrome is the most commonly diagnosed sex chromosome disorder 
among males. It is usually associated with 47 chromosomes, including two Xs and 
one Y. The formal cytogenetic designation for Klinefelter syndrome is 47, XXY; 
the extra sex chromosome is due to meiotic chromosomal nondisjunction. Increased 
risk of various malignant diseases has been recognized among patients with 
different congenital chromosomal abnormalities. Since the early 1960s, numerous 
reports have appeared of an increased risk of malignant neoplasms among patients 
with Klinefelter syndrome. Evidence suggests a correlation with increased 
incidences of germ cell tumors and breast cancers. Whether these patients are at 
an increased risk of hematologic malignant disease, especially acute leukemia, 
is still uncertain. This report describes a patient with agnogenic myeloid 
metaplasia and Klinefelter syndrome, an association not previously reported.