For years, a clinical relationship between allergic rhinoconjunctivitis (AR/C) and asthma has been observed. Recently, evidence supporting this link has been published. An important body of evidence for a real link between the two conditions has come from epidemiological studies. An increasing prevalence of both conditions is noted in the developed and developing countries. A number of studies have documented the co-existence of AR/C and asthma, with one group reporting up to 80% of patients with asthma having AR/C. Increased bronchial hyperresponsiveness, one of the characteristic findings in asthma, is also demonstrated in those with AR/C even in the absence of clinical asthma. There are a number of common factors linking the two conditions. Atopy is a risk factor for the development of both asthma and AR/C, as is the finding of positive skin tests to common aeroallergens. There is also a well documented temporal relationship between the two conditions, with AR/C beginning soon before or simultaneously with asthma – an association noted in a number of studies examining large groups of subjects . Finally, there are a few studies that demonstrate treatment of one condition leading to an effect on the other – this has been particularly noted with the improvement in asthma control once AR/C has been adequately managed. Given the growing evidence of common factors between the two conditions and the frequent finding that they co-exist in the same patient, management strategies must include treatment of both the upper and the lower airway rather than focusing only on the predominant complaint.