Betalactams allergy is the first cause of drug allergy in the world. In Chile cutaneous test are performed without considering international standardizations. This review focuses in betalactam allergy diagnosis and its management. Betalactams allergic reactions can be classified according to their temporal profile, into immediate, accelerated or late reactions which coincides with symptoms and pathogenic mechanisms. Most of immediate and accelerated reactions are mediated by specific IgE, with symptoms of immediate hypersensitivity. Toxicodermies and maculo-papular exanthemas are expression of late reaction, late hypersensitivity is probably the main mechanism in the pathogenesis of these reactions. Allergens which cause immediate hypersensitivity reactions to betalactams can be major determinants (75% of the cases), minor determinants or the side chains of the suspected drugs. The study of allergic patients includes specific IgE, skin and challenge tests. The objectives of his evaluation are to detect crossed reactivities or uni-sensibilizations, and to authorize or forbid the utilization of a specific drug or its alternatives.