The records of 89 patients who underwent surgery for solitary or multiple parenchymal brain metastases of lung cancer at the Osaka Center for Adult Diseases between 1978 and 1990 were reviewed with follow up until March 1992. The aim of this retrospective analysis was to identify prognostic features that were associated with a favourable outcome. The benefits of brain tumour surgery were evaluated in terms of the cause of death (brain metastasis, tumour in another organ, or treatment related) as well as the postoperative changes in functional state indicated by the Karnofsky scale. The overall mean survival time was 11.6 months, and the one and two year survival rates were 24% and 8%. The brain lesion itself was the cause of death in only 19% of the patients; the other 81% died of systemic disease. Functional state improved after surgical excision of the brain tumour in 36%, remained unchanged in 53%, and worsened in 11%. These data suggest that surgical intervention is beneficial for patients with parenchymal brain metastases. Variables significantly associated with a favourable prognosis included surgical excision of the primary lesion, adenocarcinoma as the histological diagnosis, the use of adjuvant treatment, especially chemotherapy, a preoperative score of over 80% on the Karnofsky scale, and metastasis confined to the brain with no extracranial metastatic foci or residual primary tumour. Additional but non-significant contributors to a good prognosis included age under 65 or 70 years, early tumour stage (stage 1), curative lung cancer surgery, a single metastatic brain tumour (v multiple lesions), a solid tumour (v cystic), and a supratentorial location of the brain metastasis. The disease free interval and the cerebrospinal fluid cytology were not significant prognostic factors. On the basis of these findings, it is concluded that the surgical removal of brain metastases of lung cancer should be undertaken if the primary tumour has already been removed whether or not there are extracranial metastases, and that postoperative chemotherapy should generally be given.