Objectives: Assessing functional impairment is one of the essential components in the clinical evaluation of ADHD in adulthood, serving both diagnostic and outcome evaluation purposes. However, clinicians and researchers may face challenges in selecting suitable instruments due to variations in accessibility and quality of instruments. Methods: We conducted an online survey involving an international group of 92 respondents engaged in clinical practice and/or research on ADHD. The survey aimed to evaluate current practices in assessing impairment in adult ADHD and related disorders, while also identifying areas requiring adaptation or potential new developments. Results: Our findings revealed that clinicians and researchers utilize a diverse range of instruments for assessing impairment in adults with ADHD, including some that may lack adequate properties for this purpose. Notably, dissatisfaction with current practice standards was expressed, underscoring the need for novel assessment approaches and improved psychometric properties. Conclusion: It is evident that research endeavors are warranted to either refine existing measures or devise new ones for assessing functional impairment in adult ADHD. Emphasis should be placed on disseminating instruments that enhance accessibility in both research and clinical settings, and facilitate streamlined administration and interpretation.