A follow-up study was conducted among men and women aged 55 years and over living in the community in order to estimate the incidence of initiation of antidepressant drug use and the association with chronic diseases. The study population consisted of 7,812 individuals. Overall, the incidence density for starting therapy with an antidepressant drug was 13.5 per 1000 person-years. The cumulative incidences after 1, 2 and 3 years were 1.3, 2.7 and 4.0%, respectively. The incidence in women was almost twice that in men and slightly higher in participants older than 70 years than in those younger than 70 years. The majority of the antidepressants prescribed were tricyclic antidepressants (65%), followed by selective serotonin reuptake inhibitors (23%) and other (12%) antidepressants. Only a minority (23%) received a dose considered effective for the indication of depression. Selective serotonin reuptake inhibitors were more often prescribed in an adequate dosage (68%) than were tricyclic antidepressants (12%) and other antidepressants (8%). Of the chronic diseases studied, only osteoarthritis and a history of stroke were predictors of initiation of antidepressant drug use after adjustment for age, sex and medical consumption. Hypertension, history of myocardial infarction, diabetes mellitus, rheumatoid arthritis, glaucoma, cognitive impairment and Parkinson's disease were not associated with future antidepressant drug use. No relevant differences were observed with respect to the choice of type of antidepressant drug among patients with chronic diseases. The present study indicates that each year antidepressant drug therapy is initiated in approximately 1.3% of the elderly. In general, the presence of chronic somatic diseases was not predictive of initiation of antidepressant drugs. Tricyclic antidepressants in this age group and in patients with certain chronic diseases may not be the optimal choice given their side-effects profile and drug-drug and drug-disease interactions. The predominance of these agents in the present study calls for further attention.