Importance: The high prevalence of hypertension among the US black population is a major contributor to disparities in life expectancy; however, the causes for higher incidence of hypertension among black adults are unknown. Objective: To evaluate potential factors associated with higher risk of incident hypertension among black adults. Design, Setting, and Participants: Prospective cohort study of black and white adults selected from a longitudinal cohort study of 30 239 participants as not having hypertension at baseline (2003-2007) and participating in a follow-up visit 9.4 years (median) later. Exposures: There were 12 clinical and social factors, including score for the Southern diet (range, -4.5 to 8.2; higher values reflect higher level of adherence to the dietary pattern), including higher fried and related food intake. Main Outcomes and Measures: Incident hypertension (systolic blood pressure ≥140 mm Hg, diastolic blood pressure ≥90 mm Hg, or use of antihypertensive medications) at the follow-up visit. Results: Of 6897 participants (mean [SD] age, 62  years; 26% were black adults; and 55% were women), 46% of black participants and 33% of white participants developed hypertension. Black men had an adjusted mean Southern diet score of 0.81 (95% CI, 0.72 to 0.90); white men, -0.26 (95% CI, -0.31 to -0.21); black women, 0.27 (95% CI, 0.20 to 0.33); and white women, -0.57 (95% CI, -0.61 to -0.54). The Southern diet score was significantly associated with incident hypertension for men (odds ratio [OR], 1.16 per 1 SD [95% CI, 1.06 to 1.27]; incidence of 32.4% at the 25th percentile and 36.1% at the 75th percentile; difference, 3.7% [95% CI, 1.4% to 6.2%]) and women (OR, 1.17 per 1 SD [95% CI, 1.08 to 1.28]; incidence of 31.0% at the 25th percentile and 34.8% at the 75th percentile; difference, 3.8% [95% CI, 1.5% to 5.8%]). The Southern dietary pattern was the largest mediating factor for differences in the incidence of hypertension, accounting for 51.6% (95% CI, 18.8% to 84.4%) of the excess risk among black men and 29.2% (95% CI, 13.4% to 44.9%) of the excess risk among black women. Among black men, a higher dietary ratio of sodium to potassium and an education level of high school graduate or less each mediated 12.3% of the excess risk of incident hypertension. Among black women, higher body mass index mediated 18.3% of the excess risk; a larger waist, 15.2%; less adherence to the Dietary Approaches to Stop Hypertension diet, 11.2%; income level of $35 000 or less, 9.3%; higher dietary ratio of sodium to potassium, 6.8%; and an education level of high school graduate or less, 4.1%. Conclusions and Relevance: In a mediation analysis comparing incident hypertension among black adults vs white adults in the United States, key factors statistically mediating the racial difference for both men and women included Southern diet score, dietary ratio of sodium to potassium, and education level. Among women, waist circumference and body mass index also were key factors.