Introduction: Spontaneous regression of cancer is defined as a complete or partial, temporary or permanent disappearance of tumor in the absence of specific therapy. With only a few cases reported, spontaneous regression is extremely rare in primary lung cancer. Regarding spontaneous regression in lung cancer, recent investigations revealed the role of immunological mechanisms, thus indicating potential treatment options by specific immunotherapy in the future. Case presentation: A 76-year-old Caucasian man with progressive dyspnea presented to our hospital. A computed tomography scan revealed a tumor mass in the upper lobe of his right lung and enlarged mediastinal lymph nodes. A biopsy of a paratracheal lymph node by mediastinoscopy disclosed metastatic lung cancer. By immunohistochemical findings the tumor was classified as large cell carcinoma. Diagnosed with clinical stage IIIA non-small cell lung cancer, a neoadjuvant therapy concept was indicated. However, before starting chemoradiation, a computed tomography scan showed a regression of both the tumor mass in the upper lobe of his right lung and the mediastinal lymphadenopathy. As a repeated computed tomography scan showed further regression, we agreed with our patient to perform routine follow-up instead of starting therapy. To date, no relapse has been reported. Conclusions: Given the circumstances that regression started after the biopsy and involved both the tumor in the upper lobe of his right lung and the mediastinal lymph node metastases, an immune response is a reasonable explanation for the observed spontaneous regression in this case.