The prognostic significance of extracranial distant metastasis detected by positron emission tomography (PET) was investigated in patients with non-small cell lung cancer (NSCLC). Forty-two patients staged with 18F-fluorodeoxyglucose-PET-detected distant metastasis before planned surgery (n = 7) or radical radiotherapy (RT)/chemoradiotherapy (n = 35) for NSCLC were identified from a prospective database. The influence of metastasis number and other prognostic factors was investigated using Cox's regression analysis. Treatment after PET included surgery (n = 2), radical RT (n = 5), palliative RT (n = 25), chemotherapy (n = 8) or supportive care (n = 2). All but 4 patients had died by the last follow-up. Median survival was 9 months overall, 12 months for 27 patients with single PET-detected metastasis and 5 months for 15 patients with > 1 metastasis (p = 0.009). It was found that the Eastern Cooperative Oncology Group performance status (p = 0.027) but not pre-PET stage, weight loss or metastasis site correlated with survival. PET-detected metastatic tumor burden appeared to influence survival and should be evaluated as a prognostic factor in NSCLC.