SAS115359: A 6-month Study to Assess the Safety and Benefit of Inhaled Fluticasone Propionate/Salmeterol Combination Compared With Inhaled Fluticasone Propionate in the Treatment of Adolescents and Adults (12 Years of Age and Older) With Asthma.

Inclusion Criteria: * Provided consent to participate in the study * Male or female, 12 years of age and older * Clinical diagnosis of asthma for at least 1 year prior to the randomization * Clinic PEF of greater than or equal to 50% of predicted normal value * Subject must be appropriately using one of the treatments for asthma listed in the protocol * Subject must be able to complete the asthma control questionnaire, daily questions about asthma, and use a DISKUS inhaler * Subject must have history of at least 1 asthma exacerbation including one of the following in the year prior to randomization: * requiring treatment with systemic corticosteroids * an asthma-related hospitalization Exclusion Criteria: * History of life threatening asthma defined for this protocol as asthma episode that required intubation and/or was associated with hypercapnea requiring non-invasive ventilatory support * Concurrent respiratory disease other than asthma * Current evidence of, or ever been told by a physician that they have chronic bronchitis, emphysema, or chronic obstructive pulmonary disease. * Exercise induced asthma (as the only asthma-related diagnosis) not requiring daily asthma control medicine * Presence of a bacterial or viral respiratory infection that is not resolved at randomization * An asthma exacerbation requiring systemic corticosteriods within 4 weeks of randomization or more than 4 separate exacerbations in the 12 months preceding randomization * More than 2 hospitalizations for treatment of asthma in the 12 months preceding randomization * Subject must not meet unstable asthma severity criteria as listed in the protocol * Potent cytochrome P450 3A4 (CYP3A4) inhibitors within the last 4 weeks (e.g., ritonavir, ketoconazole, itraconzole) * Pregnancy, breast-feeding or planned pregnancy during the study * A Child in Care (CiC) is a child who has been placed under the control or protection of an agency, organisation, institution or entity by the courts, the government or a government body, acting in accordance with powers conferred on them by law or regulation.