There is a large body of anecdotal evidence from sub-Saharan Africa of widespread medical distrust leading to health program failures. In this paper, to isolate an exogenous variation in trust in medicine to explain contemporary health demand in sub-Saharan Africa, we rely on a widespread historical shock: the slave trade. We combine Nunn and Wantchekon's (2011) historical data on the slave trade by ethnic group with geolocated individual-level data at the district level from the 2010-2014 Demographic and Health Surveys to examine the reduced-form relationship between ancestors' exposure to the slave trade and children vaccination status against measles. Exploiting within-district variation, we find that children from mothers whose ancestors were exposed to the slave trade are less likely to be vaccinated. The effect is larger than that of standard determinants of health demand, such as education or revenue. Falsification tests, exploiting other health behaviors, show that the slave trade affects demand for vaccination only through trust in medicine. We then provide explanations for the persistent effect of the slave trade on trust in medicine. We find large treatment heterogeneity along a set of important characteristics linked to cultural transmission, in particular matrilineal lineage systems, which shows that the transmission mechanism is not necessarily monotonically increasing in the exogenous material payoffs associated to mistrust. We also point to the similarity of the environment across generations, due to colonial and contemporaneous abusive medical treatments, to explain persistence of optimal mistrusting behavior.