Summary Background VEGFR-2 has a role in gastric cancer pathogenesis and progression. We assessed whether ramucirumab, a monoclonal antibody VEGFR-2 antagonist, in combination with paclitaxel would increase overall survival in patients previously treated for advanced gastric cancer compared with placebo plus paclitaxel. Methods This randomised, placebo-controlled, double-blind, phase 3 trial was done at 170 centres in 27 countries in North and South America, Europe, Asia, and Australia. Patients aged 18 years or older with advanced gastric or gastro-oesophageal junction adenocarcinoma and disease progression on or within 4 months after first-line chemotherapy (platinum plus fluoropyrimidine with or without an anthracycline) were randomly assigned with a centralised interactive voice or web-response system in a 1:1 ratio to receive ramucirumab 8 mg/kg or placebo intravenously on days 1 and 15, plus paclitaxel 80 mg/m2 intravenously on days 1, 8, and 15 of a 28-day cycle. A permuted block randomisation, stratified by geographic region, time to progression on first-line therapy, and disease measurability, was used. The primary endpoint was overall survival. Efficacy analysis was by intention to treat, and safety analysis included all patients who received at least one treatment with study drug. This trial is registered with ClinicalTrials.gov , number NCT01170663 , and has been completed; patients who are still receiving treatment are in the extension phase. Findings Between Dec 23, 2010, and Sept 23, 2012, 665 patients were randomly assigned to treatment—330 to ramucirumab plus paclitaxel and 335 to placebo plus paclitaxel. Overall survival was significantly longer in the ramucirumab plus paclitaxel group than in the placebo plus paclitaxel group (median 9·6 months 95% CI 8·5–10·8 vs 7·4 months 95% CI 6·3–8·4, hazard ratio 0·807 95% CI 0·678–0·962; p=0·017). Grade 3 or higher adverse events that occurred in more than 5% of patients in the ramucirumab plus paclitaxel group versus placebo plus paclitaxel included neutropenia (133 41% of 327 vs 62 19% of 329), leucopenia (57 17% vs 22 7%), hypertension (46 14% vs eight 2%), fatigue (39 12% vs 18 5%), anaemia (30 9% vs 34 10%), and abdominal pain (20 6% vs 11 3%). The incidence of grade 3 or higher febrile neutropenia was low in both groups (ten 3% vs eight 2%). Interpretation The combination of ramucirumab with paclitaxel significantly increases overall survival compared with placebo plus paclitaxel, and could be regarded as a new standard second-line treatment for patients with advanced gastric cancer. Funding Eli Lilly and Company.