OBJECTIVE: To examine ethnic differences in appointment-keeping in a managed care setting. DATA SOURCES/STUDY SETTING: Kaiser Permanente Diabetes Study of Northern California (DISTANCE), 2005-2007, n = 12,957. STUDY DESIGN: Cohort study. Poor appointment-keeping (PAK) was defined as missing >1/3 of planned, primary care appointments. Poisson regression models were used to estimate ethnic-specific relative risks of PAK (adjusting for demographic, socio-economic, health status, and facility effects). DATA COLLECTION/EXTRACTION METHODS: Administrative/electronic health records and survey responses. PRINCIPAL FINDINGS: Poor appointment-keeping rates differed >2-fold across ethnicities: Latinos (12 percent), African Americans (10 percent), Filipinos (7 percent), Caucasians (6 percent), and Asians (5 percent), but also varied by medical center. Receiving >50 percent of outpatient care via same-day appointments was associated with a 4-fold greater PAK rate. PAK was associated with 20, 30, and 40 percent increased risk of elevated HbA1c (>7 percent), low-density lipoprotein (>100 mm/dl), and systolic blood pressure (>130 mmHg), respectively. CONCLUSIONS: Latinos and African Americans were at highest risk of missing planned primary care appointments. PAK was associated with a greater reliance on same-day visits and substantively poorer clinical outcomes. These results have important implications for public health and health plan policy, as primary care rapidly expands toward open access to care supported by the patient-centered medical home model.