Allergic conjunctivitis, unlike several other ocular diseases, is seldom followed by permanent visual impairment; nevertheless, it is important because of both its frequency and its severity. Two major forms, seasonal and perennial, are considered in this review. To recognise the hallmarks of allergic conjunctivitis, clinicians have need of a thorough knowledge of its pathophysiological aspects and clinical features, enabling them to choose the best and most suitable therapy among the alternatives. The aims of treatment vary according to the symptoms, severity and characteristics of the allergic reactions; in general, treatment is based mainly on environmental control, pharmacotherapy and (sometimes) specific immunotherapy. Topical vasoconstrictors, decongestant compounds, standard antihistamines or combinations of these drugs have been used for a number of years to treat the acute and/or persistent symptomatology, and in order to prevent the side effects of a prolonged treatment with topical glucocorticosteroids. Nevertheless, the latter represent the most powerful anti-inflammatory drugs, and are particularly recommended in short term treatment (5 to 7 days) in severe acute symptomatology. Orally administered 'classic' antihistamines, i.e. histamine H1-receptor antagonists, are effective and very convenient in either short or long term treatment, largely because the new compounds also act on the inflammatory process secondary to the allergic events. Recently, other topical compounds such as sodium cromoglycate (cromolyn sodium), nedocromil and nonsteroidal anti-inflammatory drugs (NSAIDs) [i.e. piroxicam, aspirin] have become available. Sodium cromoglycate and nedocromil act as prophylactic compounds, able to prevent the allergic reaction; NSAIDs represent a valid and effective alternative to glucocorticosteroids in several situations.