Despite its relevance for quality care initiatives, the field of psychiatry has little scientific knowledge regarding the course of current major depression when primary care patients with the disorder remain undetected. Using statewide telephone screening, we identified and followed 98 adults with current major depression who made one or more visits to a primary care physician during the 6 months following baseline. Thirty-two percent of primary care patients with current major depression remained undetected for up to 1 year. Almost half of undetected patients developed suicidal ideation. Less than one-third of undetected patients made a visit during the month they reported their worst symptoms. Fifty-three percent of undetected patients reported five or more current symptoms at 1 year follow-up. Primary care patients with undetected major depression report persistently poor outcomes. Comparison of outcomes with detected patients suggests that quality improvement efforts directed at improving detection without improving management of detected patients may not improve outcomes.