bstract Background Attention-deficit/hyperactivity disorder (ADHD) is now acknowledged as a significant public health concern, a persistent neurodevelopmental disorder. It poses challenges across various life domains, persisting into adulthood, and is often undiagnosed. From July 2023 to December 2023, this study investigated the prevalence, types, participants’ knowledge and perceptions, and demographic determinants of undiagnosed adult ADHD among undergraduate medical students in Pakistan. Methods This cross-sectional study enrolled 342 undergraduate medical students who fulfilled the selection criteria. The data was collected using an online self-administered survey consisting of three main parts using the WHO 18-question Adult ADHD Self-Report Scale, Version 1.1 (ASRS-v1.1), to assess adult ADHD symptoms. Data analysis was conducted using SPSS (version 26.0). Results 119 medical students, or 34.8%, had adult ADHD. Inattentive dominance was the most prevalent presentation at (86, 72.3%), followed by mixed dominance at (20, 16.8%), and hyperactive dominance at (13, 10.9%). There was a statistically significant (p < 0.05) association between individuals who screened positive for adult ADHD and had co-occurring psychological disorders (e.g., anxiety, depression) and a family history of psychiatric disorders (e.g., ADHD, generalized anxiety disorder, bipolar disorder). Additionally, these individuals perceived that individuals with adult ADHD could live a normal life despite their condition. While the type of ADHD was significantly associated with the use of medications for psychological disorders, it was significantly higher among hyperactive dominants (5,71.4%), and the family history of GAD was significantly higher (2,10.0%) among mixed dominants. Conclusion This study reveals a significant prevalence of undiagnosed adult ADHD and an inattentive dominance among medical students in Pakistan, highlighting gaps in awareness and screening. These findings emphasize the crucial need for implementing ADHD screening programs. Keywords: Adult ADHD, undergraduate medical students, Prevalence, Screening, The WHO 18-question adult ADHD self-report Scale Version 1.1, Pakista