BACKGROUND Giant cell tumor is a rare tumor of mesenchymal origin. According to World Health Organization classification, it is considered a benign tumor with locally aggressive characteristics and the capacity to metastasize. The tumor typically occurs in the epiphyseal regions, most often of long bones after the completion of bone growth. The disease is characterized by severe pain and swelling of the affected area. Tumor growth is expansive but relatively slow. The tumor rarely metastasizes, but when it does, the lungs are primarily affected. CASE REPORT A 28-year-old man, otherwise healthy, presented with pain in the right wrist joint, limited range of motion, and spindle-shaped thickening/swelling in the same area, which he had noticed several months earlier. After a comprehensive diagnostic evaluation (wrist X-ray, computed tomography, magnetic resonance imaging, ultrasound-guided biopsy, and histopathological analysis), he was diagnosed with giant cell tumor of the right ulna. The tumor was surgically removed with good recovery, and the patient continued to be seen thereafter in regular followup. CONCLUSIONS The wide range of benign and malignant differential diagnostic entities requires a detailed diagnostic approach and comprehensive assessment, using different radiological modalities, as was done in this case. The final diagnosis was confirmed by histopathological analysis of core biopsy material.