This paper examines community effects on health knowledge in a developing country setting. We examine knowledge about the etiology and prevention of child illnesses using a unique 2002 representative survey of communities and households in Ghana. We find that community context matters appreciably, even after adjusting for the anticipated positive effects of an individual's education, literacy, media exposure and household socioeconomic status. The proportion of literate adults and the presence of a market in a community positively influence a person's health knowledge. In other words, even if a person herself is not literate, living in a community with high levels of literacy or a regular market can still positively affect her health knowledge. Our results suggest that social networks and diffusion play a key role in these community effects. In turn, these results offer policy implications for Ghana and sub-Saharan Africa.