Miliary brain metastasis from the lung is uncommon and has a poor therapeutic response. We report a case of pulmonary adenocarcinoma combined with multiple brain cystic lesions that were initially misdiagnosed as neurocysticercosis. A 53-year-old male who never smoked was admitted to our hospital with complaints of agitation and cognitive impairment. Brain magnetic resonance imaging showed innumerable, small nodular lesions with a central, low signal intensity in whole brain parenchyma. His symptoms were not improved by the empirical praziquantel medication for disseminated neurocysticercosis. After a transbronchial biopsy from the right middle lobe, we could diagnose the primary lung adenocarcinoma with a single nucleotide polymorphism in the epidermal growth factor receptor exon 20 at codon 787 (Q787Q). His neurologic symptoms and imaging findings have been gradually improving with a first-line Gefitinib treatment for five months. We recommend a more active diagnostic approach including biopsy in case of atypical imaging findings.