The MentDis_ICF65+ Project is an epidemiological study of mental disorders in people 65 to 85 years old in several European cities, including Madrid. Its aim is to determine the lifetime, 12-month, and 1-month prevalence of the main mental disorders in the elderly. The relationship of age and sex with each mental disorder was examined. The sample was collected through random sampling of people over 65 in Madrid, and consisted of 555 persons between 65 and 85 years old. The CIDI65+ was administered. Estimates of prevalence and odds ratios (OR) were made using sample frequencies and according to sex and age. Excluding nicotine dependence, 40.12% of the sample was found to have suffered a mental disorder at some time in their lives, 29.89% in the past year, and 17.70% were currently suffering from a mental disorder. The disorders with the highest prevalence rates were anxiety disorders, alcohol-related disorders, and mood disorders. Elderly women had a higher risk of suffering an anxiety disorder (OR men/women 0.42; CI 0.25–0.68) with a significance level of p < .001, while elderly men were more affected by any substance-related disorder (OR men/women 3.96; CI 1.62–11.07) with a significance level of p < .001. Each disorder’s prevalence decreased with age (OR 65–74/75–85, 1.85; CI 1.25–2.75) with a significance level of p < .01. Results show higher prevalence rates than previous studies reported. The main implications of this study, and the need to adapt mental health services for people over 65, are highlighted.