OBJECTIVES: The use of antidepressants has increased over the years, which may be due to more new antidepressant users, but also may be due to a longer duration of use. We aimed to assess the prevalence, incidence and average duration of selectiveerotonin reuptake inhibitor (SSRI) and tricyclic antidepressant (TCA) use in the Netherlands during 1992-2001. In addition, we assessed the incidence of long-term use of SSRIs and identified possible determinants of long-term use. METHODS: We assessed prevalence (number of current users of an antidepressant per 1000 persons assessed on a single day) and incidence (number of new users per 1000 persons per year) of antidepressant use for each year in the PHARMO record linkage system. Long-term use was defined as the consecutive use of any antidepressant for at least 12 months. Relative risks and hazard ratios were calculated and adjusted for possible determinants using Poisson and Cox regression analyses. RESULTS: Both prevalent and incident use of SSRIsincreased during 1992-2001, while TCA use remained stable. A total of 9857 patients using SSRIs were included in a follow-up study. During the follow-up period, more patients became long-term users, either directly after the start of the initial SSRI oranytime during follow-up (29.5%). The average number of days before start of long-term use decreased from 595 days in 1991 to 19 days in 1997. Female patients, older age, previous use of benzodiazepines and being treated by a psychiatrist increased theprobability of becoming a long-term user. CONCLUSION: Both prevalent and incident use of SSRIs increased during the 1990s, implicating an increased number of patients starting SSRIs, but also a longer duration of use of antidepressant therapy. Over the entire follow-up period, almost 30% of the patients became long-term users at anytime during the follow-up period.