Co-morbid mental health conditions such as anxiety and depression are extremely common in autistic adults. Vulnerability to negative life experiences such as victimisation and unemployment may be partially responsible for the development of these conditions. Here we measure the frequency of negative life experiences in autistic adults and explore how these are associated with current anxiety and depression symptoms and life satisfaction. We developed the Vulnerability Experiences Quotient (VEQ) through stakeholder consultation. The VEQ includes 60 items across 10 domains. Autistic adults with a clinical diagnosis and non-autistic controls completed the VEQ, screening measures for anxiety and depression, and a life-satisfaction scale in an online survey. Likelihood of experiencing each VEQ event was compared between groups, using binary logistic regression. Mediation analysis was used to test whether total VEQ score mediated the relationship between autism and (1) depression (2) anxiety and (3) life satisfaction. Autistic adults (N = 426) reported higher rates of the majority of events in the VEQ than non-autistic adults (N = 268). They also reported more anxiety and depression symptoms and lower life satisfaction. Group differences in anxiety, depression and life satisfaction were partially mediated by VEQ total score. This study highlights several important understudied areas of vulnerability for autistic adults, including domestic abuse, contact with social services (as parents) and financial exploitation and hardship. Improved support, advice and advocacy services are needed to reduce the vulnerability of autistic adults to negative life experiences, which may in turn improve mental health and life satisfaction in this population. Autism Res 2019, 12: 1516-1528. © 2019 The Authors. Autism Research published by International Society for Autism Research published by Wiley Periodicals, Inc. LAY SUMMARY: This study investigated whether autistic adults are more vulnerable to certain negative life experiences, and whether these experiences are related to anxiety, depression and life satisfaction. We found that autistic adults are more vulnerable to many different negative life events, including employment difficulties, financial hardship and domestic abuse. Negative life experiences partially explained the higher rates of anxiety and depression symptoms and lower life satisfaction in autistic adults compared to non-autistic adults. Improved support services are required to reduce the vulnerability of autistic adults. Reducing vulnerability may improve mental health and increase life satisfaction in this population.