What exactly is a genetic disease? For a phrase one hears on a daily basis, there has been surprisingly little analysis of the underlying concept. Medical doctors seem perfectly willing to admit that the etiology of disease is typically complex, with a great many factors interacting to bring about a given condition. On such a view, descriptions of diseases like cancer as geneticseem at best highly simplistic, and at worst philosophically indefensible. On the other hand, there is clearly some practical value to be had by classifying diseases according to theirpredominant cause when this can be accomplished in a theoretically satisfactory manner. The question therefore becomes exactly how one should go about selecting a single causal factor among many to explain the presence of disease. When an attempt to defend such causal selection is made at all, the standard accounts offered (Koch's postulates, Hill's epidemiological criteria, manipulability) are all clearly inadequate. I propose, however, an epidemiological account of disease causation which walks the fine line between practical applicability and theoretical considerations of causal complexity and attempts to compromise between patient-centered and population-centered concepts of disease. The epidemiological account is the most basic framework consistent with our strongly held intuitions about the causal classification of disease, yet it avoids the difficulties encountered by its competitors.