Introduction. The authors evaluated the application of 18 Ffluoro-2-deoxy-D: -glucose positron emission tomography/computed tomography to diagnose the activity in patients with chronic sarcoidosis. Material and Methods. The study sample included 71 patients (48 females and 23 males, their mean age being 47?3 years) with biopsy-proven sarcoidosis of chronic course. Results. All patients underwent 18 F-fluoro-2-deoxy-D: -glucose positron emission tomography/computed tomography, which detected inflammation in 65 patients (91.5%) (maximum standardized uptake value, 8.1 ? 3.9). Angiotensin-converting enzyme levels were significantly higher in the patients with positive than in those with negative 18 F-fluoro-2-deoxy-D: -glucose positron emission tomography/ computed tomography results. Conclusion. 18 F-fluoro- 2-deoxy-D: -glucose positron emission tomography/computed tomography revealed the functional inflammatory active localizations in chronic sarcoidosis. The obtained results contribute to the adequate therapeutic option.