OBJECTIVES: To determine whether depression is treated differently in older and younger patients in primary care clinics. DESIGN: Administrative data were used to identify patients with a depression diagnosis code. The sources of data were baseline and 3-month follow-up surveys, the health plan electronic database, and chart audits. SETTING: Nine primary care clinics owned by a health maintenance organization in the Midwest. PARTICIPANTS: The study sample (N=1023) consisted of adult patients, aged 19 to 93, and was divided into six age groups, from young adult, under age 35, to old old, 75 or older. MEASUREMENTS: Independent variables were a series of dummy variables: age groups, baseline depression severity, sex, and incident depression. Outcomes were defined as care processes (assessment, resources) and improvement in depression symptoms (Center for Epidemiologic Studies-Depression scale short form). Univariate and multivariate logistic regression analyses were used to analyze patient characteristics, depression symptoms, and care process variables. Significance level was reported based on the chi-square test of probability, P