The primary objective is to compare the efficacy of Symbicort Single inhaler Therapy with treatment according to conventional best practice in adolescent and adult patients with persistent asthma.

Inclusion Criteria:

• Minimum of 3 months documented history of asthma, diagnosed according to the American Thoracic Society (ATS) definition.
• Prescribed inhaled GCS at a dose of ≥320 µg/day and within the approved label for the relevant drug during the last 3 months prior to Visit 1.

Exclusion Criteria:

• Use of any b-blocking agent, including eye-drops.
• Use of oral GCS as maintenance treatment.
• Known or suspected hypersensitivity to study therapy or excipients.
• A history of smoking ≥ 10 pack years (1 pack year = 1 pack (20 cigarettes) per day for one year or equivalent).