Schooling is significantly correlated with health status, but is the relationship causal? This paper tests the hypothesis that schooling causes differences in an important health-affecting behavior: cigarette smoking. The most striking result is that for persons with 12 to 18 years of completed schooling, the strong negative relation between schooling and smoking observed at age 24 is accounted for by differences in smoking behavior at age 17, when all subjects were still in the same grade. Causality from schooling to smoking, and by implication from schooling to health, is rejected in favor of a 'third variable' hypothesis.