Spontaneous pneumothorax (SPTx) associated with primary lung cancer is quite rare, but has been reported as the initial presentation or a complication of disease progression. Moreover, chemotherapy-related SPTx in primary lung cancer occurs at a very low frequency, accounting for less than 0.05% of all cases. Here, we report the first case of erlotinib-related SPTx in a patient with advanced lung adenocarcinoma in Korea. After 3 cycles of cisplatin-based chemotherapy as first-line therapy, erlotinib was administered as second-line treatment. Asymptomatic SPTx accompanied by a significant decrease in tumor size was observed in the left lung 7 weeks later. The patient received continuous administration of erlotinib, without additional treatment. This case showed that SPTx can occur in patients with primary lung cancer receiving erlotinib, and asymptomatic chemotherapy-related SPTx in primary lung cancer may not require therapeutic intervention.