Diffuse cerebral atrophy (CA), a frequent computed tomography (CT) finding in late-onset epilepsy, is sometimes of unknown origin or cryptogenous (CCA). From a series of 228 patients with late-onset epilepsy with diffuse CA, we excluded patients with a presumed etiology. The remaining 73 (36.8%) patients were studied for a mean of 7.2 years; 15.1% had a family history of epilepsy. CCA was cortical in 50.7%, subcortical in 6.8%, and corticosubcortical in 42.5%. Seizures, generalized in 71.2%, and focal in 28.8% were generally of low occurrence with good therapeutic response. Background EEG activity was normal in most patients. During follow-up, the clinical and EEG features remained unchanged. In a control series of 92 nonepileptic subjects with diffuse CA, CCA was noted in only 4 (4.3%). No variation in grade or distribution of CCA was noted in repeated CT scans of the two groups, except in 2 epileptic patients. Psychometric tests demonstrated no cognitive impairment during evolution. The results appear to confirm the hypothesis that late-onset epilepsy associated with CCA constitutes a syndrome that is related to the characteristics of the atrophy.