Background: The presence of immunoglobulin E (IgE), which cross-reacts with allergen components, such as profilins, polcalcins, and cross-reacting carbohydrate determinants (CCD), creates a problem when selecting patients for allergen immunotherapy by using conventional methods. The aim of this study was to evaluate the prevalence of sensitization to profilins, polcalcins, and CCDs in patients with seasonal pollen allergic rhinitis. Methods: The study was performed on a group of 112 patients with seasonal pollen allergic rhinitis, ages 14 to 55 years, with sensitization to at least one seasonal allergen (IgE > 0.7 kUA/L). The presence of IgE sensitization to recombinant (r) Bet v 2, rPhl p 12, rBet v 4, rPhl p 7, and CCDs, in addition to rBet v 1, rPhl p 1, rPhl p 5, was evaluated by using a multiparameter immunoblot. Results: Among the studied patients, 64.3, 80.4, and 41.1% were sensitized to birch, timothy grass, and mugwort pollen, respectively. Sensitization to profilins rBet v 2/Phl p 12 was demonstrated in 28.6%, to polcalcins Bet v 4/Phl p 7 in 8.9%, and to CCDs in 25%. In 29.3%, serum IgE reactivity to any of the cross-reactive components could be demonstrated. Serum IgE reactivity to rBet v 2 was always accompanied by IgE reactivity to rPhl p 12, and IgE reactivity to rBet v 4 was always accompanied by IgE reactivity to rPhl p 7. Among the patients with pollinosis co-sensitized to at least two allergen sources according to extract-based diagnosis, possible false-positive results due to sensitization to cross-reactive components were detected in 17.9%. Conclusion: Evaluation of sensitization to cross-reacting components may be useful in evaluation of patients with pollen allergy who are being assessed for allergen immunotherapy to optimize the constitution of their immunotherapy vaccines.