The syndrome of interhemispheric disconnexion has been systematically researched in 10 cases of medial and posterior callosal tumours. The cases have been documented with CT Scann and two of them were anatomically verified. Two had a complete disconnexion syndrome; another, whose lesion was situated on the forceps major, had no sign of disconnexion. In the others, the semiology was proportional to the extent of the tumour, sometimes minimal and in this case, only corresponding to an extinction of the left ear in the dichotic test, which therefore appeared in our series as the most constant sign of a transfer-trouble. Among the other signs, left tactile anomia was found in two patients, left ideomotor apraxia in three, left visual anomia in five. Seven patients had a right constructional apraxia, which was bilateral in five of them. Left agraphia was noted in five patients, among which three had also a right hand dysgraphia, whose physiopathology is discussed. Tactile alexia was noted in three patients, two had a trouble of somesthesic information's transfer, one had a pure alexia (left occipital lesion plus splenium). Signs of hemispheric independence were uncommon: one patient presented a "foreign-hand sign".