Introduction: Estimates of the prevalence of depression in people with intellectual disability range from almost nonexistent to 39%. We analyzed the outcomes of three screening instruments to find out more about the prevalence in people with mild or borderline disability. Methods: 102 Dutch individuals residing in institutions or living independently took part. The Beck Depression Inventory, the Glasgow Depression Scale and the Signaallijst Depressie voor Zwakzinnigen were used. Results: Using the standard cutoff values, the numbers of people identified as depressed by the tests were 31%, 44%, and 22%, respectively. These were high numbers, and they did not refer to the same cases. When scoring above cutoff on all three tests simultaneously was the criterion, 13.7% of the participants were identified as depressed. Conclusion: The combined use of several measuring instruments taught us that depression in people with intellectual disabilities might occur more frequently than often assumed: 13.7% might be the lower limit of its actual prevalence. People in this group still run the risk of being underdiagnosed.