In this study we have explored the presence of cross reactivity to penicillin and ampicillin in patients with immediate allergic reactions caused by amoxicillin. Skin test results with amoxicillin were positive in 66.66% and in the remaining 33.34% were negative. In 81.48% patients we observed positive results of skin tests with penicillin and/or ampicillin. Only in 14.48% of the patients we observed selective response to amoxicillin. On the basis of obtained results we conclude that sensitivity of skin tests with amoxicillin is rather moderate and confirmation of amoxicillin hypersensitivity can be obtained using skin tests with other penicillins. In our material selective amoxicillin hypersensitivity can be defined as a relatively rare phenomenon. These data should have the important implications in antibiotics' selection in patients with amoxicillin allergy.