The aim of this study was to determine the serum biotin levels in patients with hyperemesis gravidarum (HG). Ninety pregnant women with HG (mild (n = 30), moderate (n = 30) and severe (n = 30)), and 80 pregnant women without HG were included for this study. In both groups, serum biotin levels were measured. There were no statistically significant differences in demographic and clinical characteristics between the HG groups and the control group except for PUQE scores. Serum biotin levels in all hyperemesis gravidarum groups were statistically significantly lower than control group. Negative statistically significant correlation between hyperemesis gravidarum severity and serum biotin levels was noted. This is the first study that shows low serum biotin levels in women with hyperemesis gravidarum.