Cancer is an important cause of death in the United States in women of childbearing age. Approximately 1 per 1000 pregnant women will develop cancer. This review (Part II follows in this issue) examines the diagnosis, prognosis, and management of cancer during pregnancy; both in terms of the cancer's effect on the pregnancy, and the pregnancy's effect on the cancer. Some diagnostic modalities and some therapies are problematic to the fetus and placenta. However, in most cases and the pregnancy can be managed concurrently with a good outcome for the baby and without compromising the mother's prognosis.