We report 6 cases of adenocarcinoma with massive lymphocyte infiltration. This adenocarcinoma is found in 0.7% of surgically resected primary lung adenocarcinomas. The tumor was located in the peripheral portion in all cases. Lymph node metastasis was detected in 4 cases. The mean follow-up period was 49.8 months; all patients were alive without recurrence despite advanced pathologic stage. Histologically, the tumors revealed an acinar and glandular structure, and the cancer epithelium was destroyed by infiltrating lymphocytes. The lung parenchyma was destroyed by the severe inflammatory cell infiltration without dense fibrosis. Immunohistochemical staining revealed that most infiltrating lymphocytes were positive for CD3 or CD20. None of the tumors were positive for latent membrane protein-1, bcl-2, or Epstein-Barr virus-encoded small RNA-1. This type of adenocarcinoma occurs in old age, and good outcome and distinctive histologic features were observed. We refer to it as primary lung adenocarcinoma with massive lymphocyte infiltration.