The central nervous system has been examined in a consecutive autopsy material of 100 adult patients with acute (N = 67) or chronic (N = 33) leukaemia. In all patients the disease was active at the time of death, infiltrating several organs, and in 45% of the cases CNS was involved. 81% of the patients with ALL had leukaemic infiltrates in CNS, and in the total AML group they were seen in 46% (P less than 0.05). A comparison between the subtypes of the AML group revealed CNS involvement in 39% of M1 + M2 and in 69% of M4 + M5 (P less than 0.05). Only in a single case of CML was the central nervous system affected, whereas 8 of 16 patients with CLL has CNS involvement. Furthermore, other pathological findings such as haemorrhages and infarcts were registered at the time of death in 33% of all patients. Terminal neurological symptoms could be ascribed either to leukaemia, other CNS pathology or a combination of both. The rate of CNS involvement is higher than reported in similar studies, and it is supposed that this may partly be ascribed to the inclusion of the spinal cord in this investigation.