Background This study investigated the application of a newly developed neuropsychological assessment, the Wolfenbütteler Dementia Test for Individuals with Intellectual Disabilities (WDTIM) in combination with the Dementia Screening Questionnaire for Individuals with Intellectual Disabilities (DSQIID). Methods The instruments were evaluated in a prospective 2‐year follow‐up study. A total of 102 people with an intellectual disability were assessed at 6‐month intervals. Data were analysed using qualitative and statistical analyses. Results Four groups of individuals emerged from the analysis: (1) confirmed suspicion, (2) no suspicion, (3) questionable suspicion and (4) early suspicion. Significant differences were found between groups 1 and 2. The WDTIM could be administered to 90%–100% of all participants exhibiting mild‐to‐moderate intellectual disability and to 50% with severe intellectual disability . Conclusions The WDTIM was shown to have good applicability to people with mild‐to‐moderate intellectual disability and to be appropriate for detecting cognitive changes. Using the two instruments in combination achieved greater accuracy in reinforcing a dementia suspicion than did using the DSQIID alone.