The post-operative clinical course of a series of 201 patients with chronic subdural haematoma has been analyzed with respect to neomembranous organisation, cortical expansion and subdural pressure in the form of a prospective (53 cases) and retrospective (148 cases) study. With the exception of one patient (primary craniotomy and membranectomy) all other 200 cases were treated according to a standardized treatment protocol consisting of burr-hole craniotomy with (170 cases) or without (30 cases) closed-system drainage. Post-operative mortality (within one month after surgery) was 2%. There was a 4.5% recurrency rate and a 2% infection rate. Morbidity solely related to chronic subdural haematoma was 2% and was characterized by a mild neurological deficit. The level of subdural pressure had no influence on the post-operative clinical course, whereas marked intra-operative cerebral re-expansion favoured a more rapid clinical improvement. Although standard deviations were within a broad range, a nearly linear inverse relation could be assumed between the amount of peri-operative cerebral expansion and the degree of neomembranous organisation of the haematomas. Subdural neomembranes seem to represent the crucial opponents to cerebral re-expansion and they prolong the duration of neurological restitution.