This was a phase III 4-part study in multiple centres. Part I was a 26-week parallel-group, randomised, placebo-controlled period (8 weeks single-blind placebo baseline, 2 weeks double-blind titration, 12 weeks maintenance, and 4 weeks tapering off). After completing the baseline period, patients were randomised in a 1:1:1:1 ratio to 1 of 3 ESL dose levels or to placebo. Part II was a 1-year open-label extension for patients who had completed Part I. The starting dose was 800 mg once daily and could be titrated up or down at 400-mg intervals between 400 and 1200 mg. Part III was an additional 1-year open-label extension for patients who had completed Part II, had participated in the post-Part II study extension, which allowed patients to continue treatment with ESL, or had continued to take ESL in a compassionate use program. ESL starting doses were the same as received at the end of Part II, during post-Part II study extension, or under compassionate use, and could be titrated up or down at 400-mg intervals between 400 and 1200 mg once daily. Part IV was a study extension to allow patients to continue ESL treatment after the end of Part III until marketing authorisation or discontinuation of clinical development.