An 81-year-old man known to have a stable cold agglutinin syndrome pre
sented with a progressive cerebral hemorrhage. Coagulation tests revea
led prolonged APTT and prothrombin time and severely decreased factor
V activity, which could not be normalized by mixing with normal plasma
. The patient appeared refractory to substitution with fresh-frozen pl
asma, suggesting the presence of a circulating inhibitor specific for
factor V. To our knowledge, this is the first case of a lymphoprolifer
ative disease leading to a cold agglutinin syndrome and a putative inh
ibitor of factor V. In patients with paraproteinemia presenting with b
leeding diathesis, the presence of a circulating inhibitor of a specif
ic coagulation factor must be considered.