The association between educational attainment and self-assessed health is well established but the mechanisms that explain this association are not fully understood yet. It is likely that part of the association is spurious because (genetic and non-genetic) characteristics of a person's family of origin simultaneously affect one's educational attainment and one's adult health. In order to obtain an unbiased estimate of the association between education and health, we have to control for all relevant family factors. In practice, however, it is impossible to measure all relevant family factors. Sibling models are particularly appropriate in this case, because they control for the total impact of family factors, even if not all relevant aspects can be measured. I use data on siblings from a US study (MIDUS) and Dutch study (NKPS) to assess the total family impact on self-assessed health and, more importantly, to assess whether there is a family bias in the association between educational attainment and self-assessed health. The results suggest that there is a substantial family effect; about 20% of the variation in self-assessed health between siblings can be ascribed to (measured and unmeasured) family factors. Measured family factors, such as parental education and father's occupation, could account only for a small part of the family effect. Furthermore, the results imply that it is unlikely that there is substantial bias due to family effects in the association between education and self-assessed health. This strengthens the conclusions from prior studies on the association between education and self-assessed health. (Contains 3 tables and 1 figure.)