To compare the detection of transthoracic tru-cut biopsy performed on metabolically active areas in positron emission tomography (PET) for the diagnosis of lung cancer, compared to only CT scan-guided biopsy. Descriptive study. Department of Thoracic Surgery, Kayseri City Training and Research Hospital, Turkey, between December 2020 to June 2021. Patients of suspected lung cancer with pre-transthoracic biopsy chest computerised tomography and without positron emission tomography were included in Group A; while, patients with both and positron emission tomography chest computerised tomography were included in Group B. Based on the CT findings of the patients in Group A, a biopsy was obtained from the most appropriate place. The patients in Group B were evaluated by a nuclear medicine specialist and the place with the highest maximum standardised uptake value before the biopsy was marked and the area to be biopsied was determined. The malignancy detection rate was significantly higher in Group B (48/50 patients, 96%) than in Group A (36/50 patients, 72%, p=0.001). Two lesions in the Group B (4 %) and 14 lesions in the Group A (28 %) were found to give benign results (p=0.001). Biopsy was repeated in one patient of Group B, and in five patients of Group A due to an initial negative diagnosis. The sensitivity of PET/CT in predicting malignant tumor was 96%, with the positive predictive value (PPV) of 98.0%; while the sensitivity of CT was 74.5%, with PPV of 82%. Transthoracic biopsies taken by considering metabolically active areas of the mass in positron emission tomography-guided can both increase diagnosis rate and reduce the complication rate by preventing repeated biopsies. Key Words: Transthoracic biopsy, PET/CT, Metabolic active lesion, Malignant tumor.