The modern stereotype that in the Middle Ages there was a general belief that mental illness was caused by sin is reviewed. The authors examined 57 descriptions of mental illness (madness, possession, alcoholism, epilepsy, and combinations thereof) from pre-Crusade chronicles and saints' lives. In only 9 (16%) of these descriptions did the sources attribute the mental illness to sin or wrongdoing, and in these cases the medieval authors appeared to use this attribution for its propaganda value against an enemy of their patron saints, their monastery lands, or their religious values. The medieval sources indicate that the authors were well aware of the proximate causes of mental illness, such as humoral imbalance, intemperate diet and alcohol intake, overwork, and grief. The banality that, since God causes all things he also causes mental illness, was only used by medieval authors under special circumstances and in a minority of cases. It does not constitute evidence of superstitious and primitive notions about mental illness in the early Middle Ages.