Background. Rhinitis and asthma are common comorbidities. The aim of this study was to determine the risk factors for asthma and other allergic diseases in seasonal rhinitis (SR) patients. Methods. Records of 922 patients diagnosed as SR between 1991 and 2005 were evaluated retrospectively. Patients were grouped according to the results of our standard skin prick tests as follows: I-No sensitization: no sensitization to any allergen; II-Mono-pollen sensitization: sensitization to only one pollen allergen; III-Poly-pollen sensitization: sensitization to more than one pollen allergen; IV-Mite sensitization: sensitization to mite with or without any other allergen sensitization. Results. The mean age of the patients was 29.5 +/- 9.6 and 587 patients (63.2%) were females. Age at onset of SR was median 21 years (16-29 years). Of the 922 patients, 99 had no sensitization, 335 had poly-pollen sensitization, 346 had mono-pollen sensitization, and 142 had mite sensitization. The most prevalent allergens were P. pratense (85.3%) and O. europae (31.5%). No sensitization group as compared to poly-pollen sensitization group had significantly higher prevalence of asthma as a single accompanying disease (14.1%, p < 0.05). Mono-pollen sensitization was significantly associated with lower risk of any accompanying allergic disease (OR: 0.7, 95% CI 0,5-0,9) while no sensitization group (OR: 2.8, 95% CI 1.3-5.9) and mite sensitization were associated with asthma (OR: 2.3, 95% CI 1.2-4.4). Conclusion. SR is a condition that presents with different phenotypes. The group with no sensitization and mite sensitization has the highest prevalence of asthma while SR patients with mono-pollen sensitization are unlikely to have an accompanying allergic disease, including asthma.