Eighty-two persons with chronic abdominal pain, submucosal or extrinsic masses, or achalasia and 20 volunteers without symptoms were prospectively examined with endosonography to assess the incidence and features of mediastinal lymphadenopathy. In 99 persons without malignant disease, 86% were found to have paraesophageal lymph nodes by endosonography. Overall, 352 lymph nodes were found, with a mean of 3.6 +/- 2.8 SD lymph nodes per person (range, 0 to 14 lymph nodes). Increasing age and chronic pancreatitis were found to correlate with a greater number of lymph nodes. Otherwise, clinical features including quantity of tobacco use, height, weight, sex, and race did not correlate with a greater number of lymph nodes as assessed by regression analysis. The mean width and length among the lymph nodes was 4.9 +/- 2.4 mm (range, 1 to 15 mm) and 9.9 +/- 5.2 mm (range, 1 to 30 mm), respectively, with the largest lymph nodes occurring in the peritracheal and peribronchial regions. Of all subjects, 95% had a maximum lymph node width of 10 mm or less, but only 40% had a maximum lymph node length of 10 mm or less. The most common ultrasound features of these lymph nodes included a triangular or crescent-shaped and homogeneous or centrally echogenic pattern. These ultrasound characteristics were distinct from those previously described in malignant lymph nodes. In summary, a high background prevalence of mediastinal lymph nodes exists as detected by endosonography and must be considered when performing esophageal or lung carcinoma staging examinations.(ABSTRACT TRUNCATED AT 250 WORDS)