Used since 1929 in medical practice, nowadays four chemical varieties of intravascular iodine based radiocontrast media (I-RCM) are available: ionic monomers with high osmolarity, ionic dimers with low osmolarity, non-ionic monomers with low osmolarity and non-ionic iso-osmolar dimers. Increasing prescription of l-RCMs augments the number of reported hypersensitivity reactions. I-RCM induced hypersensitivity reactions can be dclasified in two types: immediate hypersensitivity reactions (IHRs - occurring within the first hour) and delayed hypersensitivity reactions (DHRs - occurring between 1 hour and 7 days). IHRs usually present as urticaria and angioedema but may associate severe respiratory and cardiovascular symptoms. Risk factors for an IHRs include a prior immediate reaction, personal history of atopic diseases (mainly asthma) and treatment with beta blocking agents. Diagnostic tests for IHRs include blood tests (serum tryptase) and skin tests (prick and intradermal) performed 2 to 6 months after IHR. High osmolarity of the I-RCM is the factor most strongly associated with IHRs. Primary prevention of IHRs involves the use of non-ionic low-osmolar or iso-osmolar agents for all intravascular procedures. DHRs are usually mild to moderate in severity, transient and self-limiting, presenting as maculopapular rash in more than 50% of cases. As with IHRs, the most important risk factor for DHRs is a previous reaction to I-RCM. Assessment of DHRs includes skin prick tests, intradermal and patch tests. Due to extensive cross-reactivity between I-RCM, a change of product is no guarantee against a repeated reaction. Current premedication procedures in patients with previous severe reactions can reduce symptoms, but may not prevent recurrent reactions.