OBJECTIVE: This study was designed to: 1) identify individuals with and without a claims diagnosis for depression who received new prescriptions for SSRI antidepressants, and 2) describe SSRI usage patterns in those with depression. METHODS: This was a retrospective database claims analysis. Medical and pharmacy claims records of patients 18-64 years from 13 United Health-affiliated health plans were examined from 1/1/93 to 12/31/97. Patients had a six-month SSRI-free period before the index SSRI prescription; their claims were examined in the six months after their index prescription. They were identified as having an ICD9 claims diagnosis for depression or not. Results were adjusted using logistic regression. RESULTS: Of 46,139 patients, 22,693 (49.1%) had a depression diagnosis, 6515 (14.1%) for major depression. A lower proportion of patients with major depression diagnoses (18.5%) achieved stable SSRI therapy (150+ days) than did those with all depression diagnoses (21%). However, a higher proportion of patients with major depression diagnoses had their therapy switched, augmented or titrated (34.8% vs. 26.8%). Paroxetine users (OR=0.53, 95% CI 0.44-0.64) and sertraline users (OR=0.59, 95% CI 0.48-0.73) were less likely to achieve stable therapy relative to fluoxetine users. They were also less likely to have their SSRI therapy augmented (OR=0.84, 95% CI 0.73-0.96 and OR=0.84, 95% CI 0.72-0.99, respectively) but more likely to switch therapy (OR=1.69, 95% CI 1.49-1.92 and OR=1.32, 95% CI 1.14-1.52). CONCLUSIONS: Approximately half the study subjects had no diagnosis for depression. Patients with major depression diagnoses received more alterations in therapy than those with all depression diagnoses. Fluoxetine treatment resulted in greater duration of therapy and less switching.