The epidemiological study of 101 SSPE cases revealed the following aspects: a) an increase in the annual SSPE incidence, in relation to the improvement of detection possibilities; b) the preponderent involvement of male children and of children having experienced measles within the first 6-18 months of life; c) the high incidence of SSPE cases in families with several children, the patient being the 2nd or 3rd sibling; d) a mean interval of 50.1 +/- 32 months between acute measles and the onset of SSPE; e) the clustering of cases in terms of the epidemic year when acute measles had occurred. There were no modifications in SSPE epidemiology during the first 6 months after the initiation of mass antimeasles vaccination.