<b><i>Background:</i></b> Our aim was to observe factors associated with <i>IL13</i> rs20541 polymorphism and other factors with or without allergic comorbidities such as subject-reported allergic rhinitis (AR) and/or allergic conjunctivitis (AC) symptoms in adult asthmatics. <b><i>Methods:</i></b> A population-based sample of Finnish adult asthma patients (<i>n</i> = 1,156) and matched controls (<i>n</i> = 1,792) filled in a questionnaire. Asthma was diagnosed based on a typical history of asthma symptoms and lung function tests. Skin prick tests with 17 aeroallergens and blood tests including analysis of interleukin 13 (IL13) rs20541 (G/A) genotypes were performed for a subsample (<i>n</i> = 193). <b><i>Results:</i></b> The proportion of asthmatics reporting AR was 61.9% and reporting AC was 40.7%. After adjustments, the presence of the <i>IL13</i> rs20541A- allele (OR 3.06, 95% CI 1.42-6.58, <i>p</i> = 0.004) or multisensitization (adjusted OR 4.59, 95% CI 1.48-14.26, <i>p</i> = 0.008) was associated with AR/AC asthma. Nasal polyps and acetylsalicylic acid-exacerbated respiratory disease was also associated with AR/AC asthma. <b><i>Conclusions:</i></b> Adult AR/AC asthma could putatively be a phenotype, characterized by the presence of atopic and/or eosinophilic factors and a high prevalence of the <i>IL13</i> rs20541A- allele. Studies on the mechanisms behind this and in other populations are needed.