The number of well-characterized hereditary and acquired hypercoagulable co
nditions is increasing, such that in many thrombophilic patients, the labor
atory can now identify a hypercoagulable condition. This review describes t
he currently known hypercoagulable states that predispose patients to venou
s, and in some instances, arterial thrombosis. For each condition, the disc
ussion includes the incidence, magnitude of the thrombotic risk in the gene
ral population in comparison with symptomatic families, synergistic interac
tions among the various hypercoagulable conditions, molecular pathogenesis,
and interpretation of laboratory test results. In addition, recommendation
s for laboratory testing are summarized.