AbstractBackgroundFamily members of patient in the intensive care unit (ICU) experience a set of problems which are entitled Family Intensive Care Units Syndrome (FICUS).ObjectivesThe aim of this study was to develop and psychometrically evaluate the FICUS Inventory (FICUSI) in Iran.MethodsThis sequential exploratory mixed method study was conducted in 2020 in two main phases. In the first phase, FICUSI was developed based on the results of an integrative review and a qualitative study. In the second phase, the psychometric properties of FICUSI, namely, face, content, and construct validity, reliability, responsiveness, interpretability, and scoring, were evaluated. The sample for the construct validity evaluation consisted of 283 ICU family members.ResultsThe primary item pool of FICUSI had 144 items and was reduced to 65 items or omitting overlapping and similar items. The scale‐level content validity index of FICUSI was 0.89. In the construct validity evaluation through exploratory factor analysis, 31 items with factor loading values more than 0.3 were loaded on two factors (namely psychological symptoms and nonpsychological symptoms) which explained 68.45% of the total variance. The Cronbach's alpha and the test‐retest intraclass correlation coefficient of FICUSI were 0.95 and 0.97, respectively.ConclusionFICUSI is a valid and reliable instrument which can be used in clinical settings and studies for FICUS assessment. Further studies for the cross‐cultural adaptation of FICUSI in other contexts are recommended.Relevance to clinical practiceHealth care providers in clinical settings can use FICUSI to assess FICUS among the family caregivers of patients in ICU. Health care providers’ better understanding of FICUS helps them understand the quality of their own services for the family members of patients in ICU.