Background <p>Previous studies have indicated that high temperatures are associated with excess mortality among individuals with mental disorders, but comprehensive evaluations of the association between high and low temperatures, extreme temperature events and mortality in patients with severe mental disorders are limited.</p> Methods <p>A time-stratified case-crossover study was conducted using mortality data from 22,342 deaths among community-based patients with severe mental disorders in western China between 2006 and 2018 (11,235 during hot seasons and 11,107 during cold seasons). Individual-level exposure to high temperatures, heat waves, low temperatures, and cold spells was assessed, and the associations between these ambient temperatures and mortality were estimated using conditional logistic regression models.</p> Results <p>High temperatures during the hot seasons were associated with a 23.66% increased risk of all-cause mortality (95% CI, 15.17%–31.66%), with effects diminishing as the lag period increased. Low temperatures during the cold seasons showed a significant association with mortality at lag day 4, peaking at 15.25% (95% CI, 3.92%–25.72%) at lag day 6. Heat waves were associated with increased mortality risk, particularly with prolonged exposure and higher temperature thresholds. Cold spells did not show a similar pattern.</p> Conclusions <p>Both heat and cold related exposures are associated with higher mortality risk in community-based patients with severe mental disorders, but their temporal patterns differ—heat has an immediate effect, whereas cold acts with a delay. Our findings suggest that these patients should be prioritized in weather-related health policies, including heat–health and cold–weather warning systems, proactive follow-up by community mental health services, and tailored protection measures during forecasted extreme temperature events.</p> Clinical trial number <p>Not applicable.</p>