Introduction:Percutaneous image-guided transthoracic needle biopsy is a safe, minimally invasive,rnaccepted, easy and accurate procedure that provides useful diagnostic information and avoids morerninvasive and expensive exploratory surgeries especially in medically treatable or unresectable cases.rnComputed tomography (CT) guided transthoracic needle biopsy involves the insertion of a needle underrnthe guidance of a CT scan to a mediastinal, pleural or pulmonary lesion from which a tissue specimen isrntaken for cytological evaluation. Any solid or cystic lesion between chest wall and mediastinum can bernbiopsied percutaneously by a needle provided that it is not accessible by a bronchoscopy. Although it is arnsafe and minimally invasive procedure, CT guided a transthoracic needle biopsy (TNB) can have somerncomplications. Although it is a well-accepted procedure worldwide with determined accuracy andrncomplication rate our study was intended to specify this hospital experience, to settle a base for anrninstitutional guidelines for selecting fit patients for CT guided transthoracic needle biopsy, for directingrnways for rapid detection of complications and management if any occurs.rnObjective:To determine the diagnostic yield, complication rate and associated factors of CT guidedrntransthoracic needle biopsy in TikurAnbessa specialized hospital, Addis Ababa University, Addis Ababa,rnEthiopia.rnMethodology:An institutional-based prospective study was conducted on all patients for whom CTrnguided TNB was done for mediastinal, pleural, pulmonary or multi-compartmental mass lesions and havernpathology result from July 2018 to July 2019 G.C. The collected data wereprocessed and analyzed usingrnIBM SPSS statistics software version 25 and it is presented by statements, figures, graphs, and tables.rnResult:CT guided transthoracic biopsy was done on 57 males (56.4%) and 44 females (43.6%) whosernmean age was 49.12 years. The location of the lesions was lung (72.28%), mediastinal (12.87%), pleuralrn(10.89%), and multi-compartmental (3.96%). Average of 3 pleural punctures were required for adequaternlesion access. A minimum of 3 and a maximum of 8 scans (mean 4.8) were taken during the proceduresrnwith a mean DLP of 159.3 mG cm. The mean time required to perform biopsy was 24.8 minutes. Thernstudy found that the cooperative patients had statistically significant lower number of scans and shortrnprocedure duration than uncooperative patients. The conclusive rate of the procedure was 76.2%.rnAdenocarcinoma was the most common pathologic result of biopsied lung lesions whereas Thymoma andrnadenocarcinoma infiltrate were the most common findings in mediastinal and pleural lesions. This studyrndidnâ€™t find statistically significant differences between the conclusive and non-conclusive patient groupsrnin terms of age, sex, lesion characteristics or technical factors. Among the 101 biopsies, 20.8% hadrncomplications of which the most common was pneumothorax 12.9% followed by alveolar hemorrhagern(5%). Complications had a strong positive correlation with the traversed aerated lung and negativerncorrelation with the mean size of the lesion along the planned trajectory.rnConclusion and Recommendation:CT-guided percutaneous transthoracic needle biopsy canrnbe performed easily and safely with patient comfort, high conclusive rate, and few associatedrncomplications. Lesion size and distance of traversed aerated lung tissue are correlated with complicationsrnbut no associated factor was found with diagnostic yield. However, it is possible that larger sample sizernand correlation with the surgical outcome and follow-up imaging could show more subtle trends. Thernprocedure can be done with low dose protocols and shorter duration provided that the patient positionrnselection and line of trajectory are settled at the pre-procedural time.