INTRODUCTION: Lung cancer is the leading cause of cancer deaths in both men and women, with 80-90% of cases caused by smoking. Small cell lung cancer accounts for 20% of all cases, and is usually treated with chemotherapy. Adenocarcinoma is the main non-small cell pathology, and is treated initially with surgery. METHODS AND OUTCOMES: We conducted a systematic review and aimed to answer the following clinical questions: What are the effects of treatments for resectable and unresectable non-small cell lung cancer? What are the effects of treatments for small cell lung cancer? We searched: Medline, Embase, The Cochrane Library, and other important databases up to May 2008 (Clinical Evidence reviews are updated periodically, please check our website for the most up-to-date version of this review). We included harms alerts from relevant organisations, such as the US Food and Drug Administration (FDA) and the UK Medicines and Healthcare products Regulatory Agency (MHRA). RESULTS: We found 86 systematic reviews and RCTs. We performed a GRADE evaluation of the quality of evidence for interventions. CONCLUSIONS: In this systematic review, we present information relating to the effectiveness and safety of the following interventions: chemotherapy (postoperative or preoperative, dose intensification), continuous hyperfractionated accelerated radiotherapy (CHART), different single-agent chemotherapy regimens, first-line palliative chemotherapy (single or multiple agents), first-line platinum (or non-platinum)-based chemotherapy, molecular-targeted therapy, non-CHART hyperfractionated radiotherapy, palliative care, prophylactic cranial irradiation, second-line chemotherapy (with single or multiple agents), second-line molecular-targeted therapy (with gefitinib or erlotinib), second-line palliative chemotherapy, and thoracic irradiation (with or without chemotherapy).