Brain metastases occur in 17 to 40% of lung carcinoma and 30 to 60% of brain metastases originate from a lung carcinoma. Brain metastasis directly influences prognosis and treatment of lung cancer. The aim of this study was to prospectively compare the findings of the neurological examination performed by a neurologist and results of double dose delayed computed tomography (CT DDD). The neurologist and radiologist were blinded to each other's results. Patients included had non-small-cell lung cancer (NSCLC) and were neurologically asymptomatic with no other cancer. From November 1993 to May 1996, 135 patients were included (126 men and 9 women). Ninety neurological examinations were normal, 34 suggested brain metastasis and 11 were abnormal but did not suggest brain metastasis. One hundred thirteen CTs were normal, 1 showed a brain metastasis and 11 were abnormal but did not evidence brain metastasis. The sensitivity, specificity, positive predictive value and negative predictive value of the neurological examination were 73, 79, 23 and 97% respectively. The presence of brain metastasis was directly related to tumor stage but not to age or histology. We suggest that brain CT DDD should be performed in stage IIIA, IIIB, IV whereas in stage I or II, the neurological examination is sufficient. However, a larger number of patients would be required to confirm these findings.