There exists a strong educational gradient in cancer risk, which has been documented in a wide range of populations. Yet relatively little is known about the extent to which education is causally linked to cancer incidence and mortality. This paper exploits a large social experiment where an education reform expanded compulsory schooling during the 1960s in Norway. The reform led to a discontinuous increase in educational attainment, which we exploit to estimate the effect of the reform on various cancer outcomes. We find little evidence that education affects overall cancer risk, as well as the most common cancer sites in isolation with two exceptions: The compulsory school reform lowered the risk of lung and prostate cancers for men. These protective effects are consistent with the idea that education reduced smoking behavior and increased the uptake of prostate cancer screening.