Nausea and vomiting are common complaints in pregnancy, occurring in more than 50% of pregnant women. Occasionally, the vomiting becomes severe and persistent enough to develop into the syndrome called hyperemesis gravidarum and sometimes requires hospitalization. A 20-year-old woman presented with hyperemesis gravidarum, which was later found to be associated with a molar pregnancy. Hyperemesis gravidarum is reported to occur in as many as 26% of molar pregnancies. Increases in the level of serum beta-human chorionic gonadotropin may be the mechanism of hyperemesis gravidarum in molar pregnancy. Hyperthyroid states linked to molar pregnancy may further exacerbate hyperemesis gravidarum. Physicians should be aware of this possibility of molar pregnancy in all patients with hyperemesis gravidarum and be familiar with the appropriate management to monitor and prevent an often-fatal trophoblastic neoplasm.