This study examined the extent to which postsecondary students endorse symptoms of Attention Deficit/Hyperactivity Disorder (ADHD) and whether experienced level of stress, depression, or anxiety are associated with higher reporting of ADHD symptoms. Students attending a combined health and counseling service completed the Conners Adult ADHD Rating Scale (CAARS), the Depression Anxiety and Stress Scale (DASS), and the Life Experiences Survey (LES). A subset also completed the Brown Attention Deficit Disorder Scale (BADDS). Findings demonstrate that the BADDS had weak specificity; 35% of never-diagnosed postsecondary students were classified as probably or very probably having ADHD based on their BAADS score. Lower false positive rates were found on the CAARS. Misdiagnosis of ADHD seems especially likely in students experiencing high levels of stress, depression, or anxiety, as these psychological conditions were associated with elevated reporting of ADHD symptoms; such conditions must therefore be considered when assessing for possible ADHD in young adults.