BACKGROUND: Controversy remains regarding the effect of needle size on the diagnostic yield of endobronchial ultrasound (EBUS)-guided transbronchial needle aspiration. We conducted a prospective study comparing the diagnostic yield of 19 and 21 G EBUS needles and hypothesized that the 19 G have a greater EBUS-guided transbronchial needle aspiration diagnostic yield as compared with the 21 G needle. METHODS: A total of 60 patients undergoing EBUS-guided transbronchial needle aspiration were enrolled with informed consent. Both 19 and 21 G needles were used at each lymph node station in alternating fashion, we randomized which needle, to begin with. Two rapid on-site cytology evaluation stations were present and assigned to one of the 2 needles. They reported sample adequacy and prepared a separate cell block per lymph node sampled for their assigned needle. RESULTS: A total of 141 lymph nodes were analyzed. Diagnosis included 69 benign lymph nodes, 47 malignant lymph nodes, 22 noncaseating granulomas, and 3 infected lymph nodes. Five hundred seventy-three passes (average: 4.1 passes/lymph node) were done with 19 G and 581 passes with 21 G needles (average: 4.1 passes/lymph node). Diagnostic yield was similar between 19 and 21 G needles overall (89.4% vs. 88.7%, P=0.71). The 19 G needles showed higher smear cellularity (32.6% vs. 13.0%, P=0.05), and rapid on-site cytology evaluation adequacy (84.8% vs. 63.0%, P=0.004) in lymph nodes with cancer diagnosis. In 7 of the 141 lymph nodes, samples from only one of the needles provided the final diagnosis. CONCLUSION: There is no difference in the overall diagnostic yield between 19 and 21 G needles. Further studies are needed to confirm the trend of the superiority of 19 G in cancerous lymph nodes.