Thromboembolic complications of pregnancy and the puerperium deserve renewed attention not only because they are the most frequent nonobstetrical complications encountered in these circumstances, but also because of current litigious attitudes, the greater survival of women with prosthetic heart valves, and the inadequacy of current treatment regimens that put the physician, as well as the patient, in special peril. New techniques are available to the clinical laboratory for studying the coagulation and hypocoagulant proteins, coagulation inhibitors, and the fibrinolytic system. They provide fresh insight into this perplexing medical problem. Attention to the details of current investigations, efforts to control the risk factors, and the perspicacious use and suitable monitoring of pharmacological agents can be expected to reduce the risks for both the pregnant patient and her attending physicians.