The surgical separation of a pair of conjoined twins in the year 1689 by Johannes Fatio was the subject of a recent article in this journal. The reference used as publication of the case was Fatio's book, Der Arzney Doctor, Helvetisch-Vernuftige Wehe-Mutter, published in 1752, although the case was presented in literature by three earlier sources. Two articles were published in the Miscellanea Curiosa sive Ephemeridum Medico-Physicarum Germanicarum Academiae Imperialis Leopoldinae Naturae Curiosorum in 1689 by Emanuel Konig and another in 1690 by Theodor Zwinger who described and illustrated the case in detail. Besides these articles, a Flug Blatt was published on the case between 1689 and 1695. Fatio copied the engraved plate in his book from Konig's engraving. These two sources should be cited as the first publications on the successful separation of Elisabet and Catherina, and not Fatio's book from 1752.