Purpose To examine mortality and causes of death in a population-based cohort of adults with autism spectrum disorder (ASD), and to compare findings with a sample drawn from the general population. Methods A population-based cohort of individuals (N = 113) born 1962-1984 and diagnosed with ASD in childhood during the 1970's and 1980's was followed up through register between 2000 and 2023. Most individuals were diagnosed with co-occurring intellectual disability (ID). The group was compared to an age- and sex-matched group (N = 1130) from the general population. Data for both groups were obtained from the National Cause of Death Register in Sweden. Kaplan-Meier survival analysis was used to calculate the survival distributions of the participants with ASD and the comparison group, and Cox proportional hazards regression to estimate Hazard ratios for mortality. Results During the study period (2000-2023) 9.7% of the ASD group and 2.7% of the comparison group had died, p < .001. The ASD group had a higher risk of mortality than the comparison group (Hazard Ratio = 3.77, 95%CI = 1.89-7.52, p < .001). Mortality did not differ significantly between males and females in the ASD group. Significantly more individuals with severe ID had died compared to the rest of the cohort, X-2 (1, N = 113) = 4.7, p < .05. Conclusion Individuals with ASD and co-occurring ID may be at greater risk of death compared to the general population. Our findings emphasize the importance of monitoring and promoting health in individuals with autism, with special attention to individuals with co-occurring ID.