A 34-year-old pregnant woman was diagnosed with pneumonia at another hospital in her 26th week of pregnancy. Antibiotics were administered, but they were not effective. She was then introduced and admitted to our hospital. Lung cancer was suspected from her chest-CT scan on admission. Caesarian section was performed on the day after admission at 33 weeks of gestation. Adenocarcinoma of the lung was diagnosed based on the results of a right-axillary lymph node biopsy performed simultaneously with the caesarian section. On the 8th day after admission, we began to administer gefitinib. We expected positive results from gefitinib, because the patient fitted the optimal profile: female, never smoker, adenocarcinoma histology. Her respiratory condition had worsened dramatically after her caesarian section, so she was given noninvasive positive pressure ventilation from the 13th day after admission. Disseminated intravascular coagulation progressed, and her chest X-ray showed bilateral extensive infiltration. Moreover, tests showed that her tumor was negative for epidermal growth factor recepter mutation, so we judged that gefitinib was not effective for her. Although her performance status was very poor, she and her family strongly desired further chemotherapy. We thus began to administer gemcitabine, but her respiratory condition deteriorated further, and she died on the 17th day after admission. Lung cancer combined with pregnancy is a very rare situation, so we report this case with some references.