Clinic and laboratory examinations were performed on a 2 year old, male, Boxer dog. The dog is believed to have a multi-systemic disease. Cytological examinations that conducted in the samples obtained by fine-needle aspiration biopsy from the dog with lymhadenopathy confirmed the diagnosis of lymphoma, which is one of commonly diagnosed neoplasms in dogs. It is concluded that definitive diagnosis of suspected neoplastic lesions in small animals can be easily made based on the results of cytological exminations of samples obtained by fine-needle aspiration.