SUMMARYOne hundred and fourteen elderly medically ill day patients were interviewed in order to assess the prevalence of DSM-111-R main psychiatric disorders. Dementia affected 14.0% of the subjects, major depression 20.3%, dysthymic disorder 4.4%, atypical depression 13.2%, other disorders 3.6%. Overall, 60.5% of the patients had a psychiatric disorder. The computerized case designation (AGECAT) showed an acceptable concordance with clinical diagnoses (kappa value for dementia 0.59, for depression 0.58). Some issues related to the high prevalence of major depression are discussed.KEY WoRDs-Elderly, medically ill, psychogeriatrics, AGECAT, GMS.Reports on the prevalence of psychiatric disorders (mainly dementia and depression) in elderly patients with medical illness are relatively scanty and prevalence rates are very varied (though generally high), ranging from 28% (Billig et al., 1986) to 42.1% (Magni et al., 1985). A large part of the variance is probably accounted for by differences in the target sample (age, type of medical illness), in methodology (questionnaire, semistructured interviews) and in the criteria for diagnosis (cut-off points, ICD-9, DSM-111, etc). As with a younger medical population, the presence of medical illness can be a serious obstacle to the detection of depressive disorders; somatic symptoms like insomnia, low energy, and loss of appetite could lead to an overestimate of depression, especially when surveys are conducted with unstandardized questionnaires (Mayou and Hawton, 1986;Rodin and Voshart,