Allergen immunotherapy (AIT) to patients with allergy towards pollens, cats or house dust mite provides longstanding improvement of symptoms of rhinoconjunctivitis and allergic asthma and reduces the need for symptomatic medication. In addition, some studies suggest that AIT can protect from the development of asthma in children with allergic rhinitis. The clinical effects of AIT are explained by a shift from a Th2 to a Th1-mediated immune response upon allergen exposure. In Sweden the treatment is given as sublingual tablets (grass) or subcutaneous injections, and a treatment period of 3-4 years is necessary to ensure longstanding effect of the treatment. Serious side-effects such as asthma attacks or anaphylaxis are uncommon, if the treatment is provided by staff specifically trained to administer AIT. Intralymphatic administration of the allergen extract is a novel and promising approach that might shorten the treatment period with similar clinical effects.