Mediastinal masses of various origins can be encountered on imaging in symptomatic or asymptomatic patients. We aimed to evaluate the diagnostic yield and complication rate of computed tomography (CT)-guided mediastinal core needle biopsies in a large population of patients presenting with mediastinal masses and to identify the factors that could influence these results. In total, 293 consecutive CT-guided mediastinal biopsies, performed in 285 patients with equivocal masses at a single center from 2006 to 2011, were included. Lesion characteristics, technical biopsy parameters, final diagnoses, diagnostic yields (number of biopsies that yielded a complete diagnosis divided by the total number of biopsies), and complication rates were recorded. Malignant diagnoses, including lymphoproliferative disorders (N=151, 53%) and lung cancers (N=54, 19%), were established in 233 cases (82%). Benign lesions were found in 52 procedures (18%), including sarcoidosis (N=19, 7%) and infections (N=17, 6%). The overall diagnostic yield was 87% and was lower for lymphoma residual masses (57%) than for initial diagnosis or relapses of known disease (90%). Complications occurred in 21 patients (7%), but only 2 patients (0.7%) required hospitalization for >12 hours. Neither the diagnostic yield nor the complication rate was influenced by the target characteristics or by technical parameters. CT-guided core needle biopsy of equivocal mediastinal masses is a minimally invasive procedure that is effective and safe, even in cases of small targets or targets in challenging locations.