Laryngeal diastema or laryngeal or posterior laryngotracheal cleft is a rare congenital malformation producing an aerodigestive communication of abnormal location which leads to severe or even fatal respiratory and infective complications. Findings in 16 cases are presented and the characteristics and particular problems of treatment of this malformation discussed. Diagnosis is presently based on results of microlaryngoscopic examination. Details are given of therapy of the commonest forms of the affection (cricoidal and upper cricotracheal), operations being performed in 9 such cases, and the place and course of forms limited to the interarytenoidal space discussed. Frequency and effect on prognosis of associated malformation are outlined. Considerable improvement has been obtained in the postoperative prognosis of cricoidal (I) and upper cricotracheal (II) forms during the last few years, and these forms must now be considered as curable.