Objective: Approximately 5% of adults have ADHD. Despite recommendations regarding the diagnosis of emerging adults, there is not a strong consensus regarding the ideal method for diagnosing ADHD in both emerging and mature adults. We were interested in determining whether a threshold of four, five, or six ADHD symptoms would be associated with significantly different levels of functional impairment and be more or less indicative of a potential ADHD diagnosis. Method: We examined the relation between functional impairment and these ADHD symptom thresholds in 2,577 college students. Results: Our findings suggest that none of these symptom thresholds are differentially better at predicting functional impairment. Conclusion: The Diagnostic and Statistical Manual of Mental Disorders (5th ed.; DSM-5) threshold of five symptoms for ages 17 years and older is not necessarily predictive of ADHD-related impairment in college students and may not be preferable to other thresholds. Options for resolving this diagnostic dilemma are discussed.