One of the pillars of efforts in the US to curb HIV incidence is pre-exposure prophylaxis (PrEP). We examined racial/ethnic and sex disparities in PrEP uptake among California Medicaid enrollees. Claims data from 2019 identified enrollees and PrEP users in each racial/ethnic, sex, and age group, yielding crude uptake rates. We then predicted age-adjusted uptake rates from multivariable logit regressions and divided PrEP uptake estimates by each group's number of new HIV diagnoses to estimate PrEP-to-need ratios. Predicted uptake was highest for White (0.29 percent) and Black (0.23 percent) males and lowest (0.16 percent) for Hispanic males. Rates for males exceeded those for females; however, Black females had twice the rate of PrEP uptake of White females. Black males and females and Hispanic males had PrEP-to-need ratios that were less than one-third (4.0-6.3) those of Asian and White males and females (14.4-19.9). Low PrEP use rates and disparities in uptake threaten efforts to end the HIV epidemic. Policy makers must craft the rollout of innovations such as PrEP in a manner that narrows HIV disparities instead of widening them.