INTRODUCTION Castleman disease was for the first time described in 1956 as a mediastinal tumour mass. Etiology of this disease is still unknown. The disease can be solitary and multicentric or rarely of a mixed type. The former is often of hyaline vascular type, while the latter is of plasma cell type. CASE REPORT Castleman disease was diagnosed in a 26-year old male patient when a well defined shadow was incidentally detected in the middle lobe of the right lung. A year before, he was diagnosed with allergic rhinitis to Ambrosia. Two years after surgery the patient was feeling well, and was without any recurrence, however, allergic rhinitis still persisted. CONCLUSION Castleman disease can occur in any organ containing lymph tissues. Most frequently the disease is described as mediastinal, rarely as an intrapulmonary tumorous mass, and it is most frequently seen in younger persons. The solitary type of Castleman disease is surgical treatable with a prospect of good prognosis, while the multicentric and mixed types recur despite treatment with cortisone, irradiation and cytostatics. As the association between Castleman disease and allergic diseases has not been confirmed up-tonow, it could be concluded that this patient suffered from two separated diseases.