Objective: To assess the associations between adherence to the Swedish dietary guidelines and all-cause mortality and thus assessing the index' ability to predict health outcomes, as well as levels of dietary greenhouse gas emissions (GHGEs). Design: A longitudinal study 1990-2016 within the population-based cohort Västerbotten Intervention Programme. Dietary data were based on food frequency questionnaires. Diet quality was assessed by the Swedish Healthy Eating Index for Adults 2015 (SHEIA15), based on the 2015 Swedish dietary guidelines. Dietary GHGEs were estimated from life cycle assessment data including emissions from farm to industry gate. Hazard ratios (HRs) and 95% confidence intervals (CIs) of all-cause mortality were evaluated with Cox proportional hazards regression, and differences in median GHGEs were tested using the Kruskal-Wallis one-way ANOVA test, between quintiles of SHEIA15 score. Setting: Northern Sweden. Participants: In total, 49,124 women and 47,651 men, aged 35-65 years. Results: Median follow-up times were 16.0 years for women and 14.7 years for men, during which time 3074 women and 4212 men died. A consistent trend of lower all-cause mortality HRs for both sexes with higher SHEIA15 scores was demonstrated. For women, the all-cause mortality HR was 0.81 [(95% CI 0.71-0.92); p=0.001] and for men 0.90 [(95% CI 0.81-0.996); p=0.041] between the quintile with the highest SHEIA15 score compared with the quintile with the lowest SHEIA15 score. A consistent trend of lower estimated dietary GHGEs among both sexes with higher SHEIA15 scores was also found. Conclusions: Adherence to Swedish dietary guidelines, estimated by SHEIA15, seems to promote longevity and reduce dietary climate impact. © The Authors 2023.