Clinical and laboratory characteristics of 39 patients with adult onset subacute sclerosing panencephalitis (SSPE) are described and compared to those of juvenile onset patients regarding preceding measles, age at onset, gender, interval between onset and diagnosis, clinical profile, and course during follow up. Diagnosis was based on clinical and electroencephalographic findings and raised anti-measles antibody titres in cerebrospinal fluid. Mean age at SSPE symptom onset was 20.9+/-4.9 years and mean interval from onset to diagnosis was 6.3+/-9.6 months. Referral diagnosis was accurate in only 12 patients. Presenting symptoms included myoclonus, behavioural changes, seizures, and cognitive, visual, and extrapyramidal disturbance. All patients received symptomatic therapy; 19 also received disease modifying agents. Five of seven pregnant women had successful deliveries. The follow-up period varied widely (maximum 60 months, median 9 months). The profile of adult onset SSPE did not differ from the rest of the cohort, except for a longer interval between measles infection and symptom onset (p<0.0001). SSPE in adults poses diagnostic challenges for clinicians. A high index of suspicion and appropriate investigations are necessary for early diagnosis and counselling.