ABSTRACT- Project 1 Suicide rates in autistic adults are alarming high in recent research; 4- 72% have endorsed suicidal ideation and 4-33% have engaged in suicidal behavior or attempts. Both scientific and advocacy groups have endorsed research for effective suicidality assessment and identification of risk factors. However, existing suicidality screening measures do not seem to function in the same way for autistic adults, and to date, no research has used a measure of suicide risk rather than a screen of imminent risk. Adaptation of existing suicide screens may be insufficient, given evidence that autistic adults may have unique risk factors, such as camouflaging of autistic traits and autistic burnout. This study will develop a suicidality measure for autistic adults, the Autism Suicidality Inventory, that will capture a continuum of suicide risk. Autistic adults and their allies will refine an item pool, and 25 autistic adults (at least 10 of which with suicidality) will complete cognitive interviews of the drafted items to ensure clarity and comprehension. A sample of 1000 autistic and non-autistic adults will complete the drafted questionnaire and a related online battery of measures to evaluate the dimensionality of the item pool, conduct Item Response Theory calibration, and compare existing suicide measures to the proposed questionnaire via IRT co-calibration. A subsample of 300 autistic and non-autistic participants (the ACE core sample) will repeat the measure every two months for a year, and cross-project analyses will examine whether those who report more suicidality baseline also report more suicidal ideation in daily life, model suicide risk over time via latent growth models, and identify factors that are most strongly associated with suicidality trajectories. The Autism Suicidality Inventory will be the first validated suicide propensity measure developed for ASD, designed with input from autistic adults and capturing a continuum of risk via an emphasis on processes that relate to risk. The availability of such a measure is essential to inform intervention development to improve safety and quality of life.