This paper deals with birth order and epilepsy. The Greenwood-Yule's method was applied, with the most powerful statistical test available, Halperin's modified chi-square. The authors concluded that there is a consistent positive association between this illness prevalence and birth order of the patients, being first and last born over-represented, irrespective of their sibship size. The data were obtained in two psychiatric hospitals in the city of São Paulo, being social class factor qualitatively controlled. All the 238 patients studied suffered a wide range of psychiatric symptoms.