Although Blacks and Whites in the United States use drugs at similar rates, Blacks are much more likely to be arrested for drug crimes. We tested the hypothesis that racial disparities in drug arrests are exacerbated in predominantly White neighborhoods.Using publicly available data we calculated the disproportion of Black arrests as a function of the proportion of Black arrests over the proportion of Black residents within the 56 police service areas that make up the Washington, DC metropolitan police department (MPD). We compared the disproportion of Black arrests with the percentage of White residents within each service area.The population within MPD jurisdiction is 50.7% Black and 38.5% White. Between July 2014 and August 2015, 87.8% of the 3329 individuals arrested for drugs were Black, yielding a citywide disproportion of Black drug arrests of 1.73. Linear regression showed a statistically significant exponential relationship between the disproportion of Black arrests and the percentage of White residents within a police service are, peaking at an arrest disproportion of 12.4 in an 84% White area.Disproportionate Black drug arrests increase with the percentage of White residents in an area. Racial bias in drug arrests may be linked to segregation.