Maternal nutrition during pregnancy has a significant effect on the health of the offspring and mother, highlighting the need for identifying factors that may affect diet during pregnancy. Research in nonpregnant and pregnant populations suggest depression may play a role. To investigate the relationship between prenatal depression and diet quality during pregnancy overall and by race/ethnicity and to explore the relationships between prenatal depression and the 12 Healthy Eating Index 2010 dietary components. A cross-sectional secondary analysis of a cohort study of Kaiser Permanente Northern California women entering prenatal care between October 2011 and April 2013. Participants included 1,160 adult pregnant women. Poor diet quality was defined as a Healthy Eating Index 2010 score in the lowest quartile. Logistic regression was used to assess the relationship between prenatal depression (defined as a depression diagnosis, Patient Health Questionnaire score of 10 or greater or antidepressant medication dispensing between the last menstrual period and completion of the food frequency questionnaire) and poor diet quality overall and by race/ethnicity. Relationships between prenatal depression and each of the 12 Healthy Eating Index 2010 dietary components were assessed using t-tests and linear regression analyses. One hundred fifty-nine (14%) participants had prenatal depression. Women with prenatal depression had nearly two times the odds of poor diet quality (odds ratio 1.80, 95% CI 1.23 to 2.60) compared with women without prenatal depression, after adjusting for potential confounders. Differences emerged by race/ethnicity; after adjusting for potential confounders the adjusted odds of poor diet quality were significant only among Hispanic women. Hispanic women with prenatal depression had an increased odds of poor diet quality compared with Hispanic women without prenatal depression (odds ratio 2.66, 95% CI 1.15 to 6.06). Women with prenatal depression had a higher consumption of empty calories (from solid fats, alcohol, and added sugars; threshold for counting alcohol >13 g/1,000 kcal) (P=0.01) and lower consumption of greens and beans (P<0.05), total fruit (P<0.01), and whole fruit (P<0.01), compared with women without prenatal depression. Except for empty calories, these findings remained after adjusting for potential confounders. Study findings suggest that women with prenatal depression are at a higher risk of poor diet quality compared with women without prenatal depression, and the relationship is stronger among Hispanic women. Nutrition counseling interventions for women with depression should consider the use of culturally sensitive materials and target limiting empty calories from solid fats, alcohol, and added sugars and encourage eating more greens, beans, and fruit.