Purpose: Previous research indicated that the Patient-Reported Outcomes Measurement Information System (PROMIS®) item bank v2.0 ‘Ability to Participate in Social Roles and Activities’ may miss subdomains of social participation. The purpose of this study was to generate items for these missing subdomains and to evaluate their content validity. Methods: A three-step approach was followed: (1) Item generation for 16 International Classification of Functioning Disability and Health subdomains currently not covered by the item bank; (2) Evaluation of content validity of generated items through expert review (n = 20) and think-aloud interviews with a purposeful sample of people with and without (chronic) health conditions (n = 10), to assess item comprehensibility, relevance, and comprehensiveness; and 3) Item revision based on the results of step 2, in a consensus procedure. Results: First, 48 items were generated. Second, overall, content experts indicated that the generated items were relevant. Furthermore, based on experts’ responses, items were simplified and ‘participation in social media’ was identified as an important additional subdomain of social participation. Additionally, ‘participating in various social roles simultaneously’ was identified as a missing item. Based on the responses of the interviewed adults items were simplified. Third, in total 17 items, covering 17 subdomains, were proposed to be added to the original item bank. Discussion: The relevance, comprehensibility and comprehensiveness of the 17 proposed items were supported. Whether the proposed extension of the item bank leads to better psychometric properties of the item bank should be tested in a large-scale field study.