Background Lifestyle interventions among people with impaired glucose tolerance reduce the incidence of diabetes, but their effect on all-cause and cardiovascular disease mortality is unclear. We assessed the long-term effect of lifestyle intervention on long-term outcomes among adults with impaired glucose tolerance who participated in the Da Qing Diabetes Prevention Study. Methods The study was a cluster randomised trial in which 33 clinics in Da Qing, China-serving 577 adults with impaired glucose tolerance-were randomised (1: 1: 1: 1) to a control group or lifestyle intervention groups (diet or exercise or both). Patients were enrolled in 1986 and the intervention phase lasted for 6 years. In 2009, we followed up participants to assess the primary outcomes of cardiovascular mortality, all-cause mortality, and incidence of diabetes in the intention-to-treat population. Findings Of the 577 patients, 439 were assigned to the intervention group and 138 were assigned to the control group (one refused baseline examination). 542 (94%) of 576 participants had complete data for mortality and 568 (99%) contributed data to the analysis. 174 participants died during the 23 years of follow-up (121 in the intervention group vs 53 in the control group). Cumulative incidence of cardiovascular disease mortality was 11.9% (95% CI 8.8-15.0) in the intervention group versus 19.6% (12.9-26.3) in the control group (hazard ratio [HR] 0.59, 95% CI 0.36-0 96; p=0.033). All-cause mortality was 28.1% (95% CI 23.9-32 4) versus 38.4% (30.3-46.5; HR 0 71, 95% CI 0.51-0.99; p=0.049). Incidence of diabetes was 72.6% (68.4-76.8) versus 89.9% (84.9-94.9; HR 0.55, 95% CI 0.40-0.76; p=0.001). Interpretation A 6-year lifestyle intervention programme for Chinese people with impaired glucose tolerance can reduce incidence of cardiovascular and all-cause mortality and diabetes. These findings emphasise the long-term clinical benefits of lifestyle intervention for patients with impaired glucose tolerance and provide further justification for adoption of lifestyle interventions as public health measures to control the consequences of diabetes.