Cerebral mycosis is a rare condition, difficult to diagnose in life, but is not easily missed at post-mortem examination. We report clinical and pathological findings in four patients with long duration prodromes, seizures and psychiatric symptoms. All of them had been misdiagnosed. Actinomycotic granules in two and Aspergillus filaments in the other patients were ascertained at histological examination. Two of the patients were in their twenties and apparently healthy. We suggest that the possibility of mycotic infection should be considered even in cases where no lowering of the body's defences can be postulated. Cell mediated immunity defects may be assumed as underlying these infections. Therefore we would suggest the importance of immunological tests for type IV immune responsiveness in all intracranial infective processes of undefined etiology.