Depression is common among older people but more common among those living in care homes. Depression is not easily detected among older adults because of the presentation, and the tendency for older people not to complain of depression, particularly those living in care homes. In general, care home staff have limited training in recognising depression. Depression is undertreated and residents may not receive a therapeutic dose of antidepressant. The true prevalence of depression among care home residents is uncertain. This feasibility study aimed to explore the level of depression among older people in care homes by comparing the outcome of an assessment by care home staff with the outcome of a diagnostic clinical interview, using ICD-10 criteria and the 30-item Geriatric Depression Scale (GDS), conducted by a psychiatrist. In all, 47 older people from four care homes were interviewed by a psychiatrist. Of them, 39.1% (18/46) of residents were prescribed an antidepressant and were no longer depressed; 8.7% (4/46) were prescribed an antidepressant and remained depressed; and 6.5% (3/46) of residents assessed as being depressed, had not been prescribed an antidepressant. That is, 54% (25/46) of residents had been or were currently depressed. Using ICD-10 criteria, the sensitivity of the GDS at a threshold of 10 and 11 was 100%. In total, 89.4% of residents received a correct diagnosis (presence or absence of depression) using the GDS at the 11 threshold. The prevalence of depression in these homes was 54%. Of the residents with depression, 72% (18/25) were managed with an antidepressant and 28% (7/25) were receiving ineffective or no treatment. The 30-item GDS can provide more useful information than a home care staff assessment for identifying depression. More research should explore the value of training home care staff to administer the 30-item GDS to optimise the management of depression in older people in care homes.