The patient was a 60-year-old woman who underwent chest wall resection for a metastatic tumor in the anterior portion of the right 3rd rib, from thyroid cancer. The anterior portion of the right 3rd rib and the 2nd and 3rd intercostal muscles were resected, and chest wall reconstruction was not performed. On the 5th postoperative day, the patient developed a pulmonary hernia. Radiologically, more than half of the right upper lobe and middle lobe were prolapsed from the resected chest wall. The patient complained of cough and dyspnea, and an emergency surgery was performed. Elevated intrathoracic pressure due to obesity was considered to be a serious risk factor of the lung hernia after chest wall resection without reconstruction.