The substantial majority of patients with asthma can expect minimal breakthrough symptoms on standard doses of inhaled corticosteroids with or without additional add-on therapies. SIMPLES is a structured primary care approach to the review of a person with uncontrolled asthma which encompasses patient education monitoring, lifestyle and pharmacological management and addressing support needs which will achieve control in most patients. The small group of patients presenting with persistent asthma symptoms despite being prescribed high levels of treatment are often referred to as having 'difficult asthma'. Some will have difficult, 'therapy resistant' asthma, some will have psychosocial problems which make it difficult for them to achieve asthma control and some may prove to have an alternative diagnosis driving their symptoms. A few patients will benefit from referral to a 'difficult asthma' clinic. The SIMPLES approach, aligned with close co-operation between primary and specialist care, can identify this patient group, avoid inappropriate escalation of treatment, and streamline clinical assessment and management.