This paper presents a model of human capital accumulation that allows for feedback effects between the consequences and the likelihood of suffering from particular diseases and the decisions to invest in knowledge, both in the form of schooling and on-the-job training. I use a calibrated version of the model to estimate the long run impact of eradicating HIV/AIDS and malaria for a number of Sub-Saharan African countries. I find that the effect on output per worker can be substantial.