Although several antineoplastic agents have been proven to be safe for the fetus after the organogenesis period, there is limited information on their use during the first trimester of pregnancy. Herein we report the first case of a patient with metastatic lung cancer treated with erlotinib during the first 2 months of an unrecognized pregnancy. A 30-year-old woman was diagnosed with stage IV non-small cell lung cancer with bone and lung metastasis. The patient received 4 months of palliative cisplatin/gemcitabine chemotherapy and biphosphonates. After 12 months the disease progressed and the patient received erlotinib 100 mg/day. During this period the patient became pregnant. Since she recalled the date of her last menstrual period at about 15 days prior to the start of the therapy, we did consider the possibility of conception at the time of the first day of erlotinib administration. Informed about the risk for the fetus due to erlotinib, the patient stopped anticancer treatment. After 42 weeks of regular gestation, cesarean section was performed, delivering a 3490 g female new-born with no evidence of congenital malformations. The disease evaluation performed with thoracic CT scan, after 1 month from the childbirth, showed a progressive lung metastasis and erlotinib treatment was resumed at the dose of 150 mg/day.