Background: Among people with spinal cord injury (SCI), minorities experience a disproportionately higher burden of diseases. Knowledge of data quality by race/ethnicity will help better design racial health disparity research and understand potential errors/biases. Objective: To investigate racial/ethnic differences in response completeness in a longitudinal SCI database. Methods: This study included 7,507 participants (5,483 non-Hispanic whites, 1,414 non-Hispanic blacks, and 610 Hispanics) enrolled in the National SCI Database who returned for follow-up between 2001 and 2006 and were aged ≥18 years at follow-up. Missing data were defined as any missing, unknown, or refusal response to interview items. Results: The overall missing rate was 29.7%, 9.5%, 9.7%, 10.7%, 12.0%, and 9.8% for the Craig Handicap Assessment and Reporting Technique-Short Form (CHART) economic self-sufficiency subscale, CAGE questionnaire, drug use, Diener’s Satisfaction with Life Scale, Patient Health Questionnaire, and pain severity, respectively. The missing rate for the CHART measure was significantly higher among non-Hispanic blacks and Hispanics than among non-Hispanic whites, after controlling for demographics, injury factors, mode of data collection, and study sites. The missing data in the other outcome measures examined were also significantly higher among non-Hispanic blacks than among non-Hispanic whites but were not significantly different between Hispanics and non-Hispanic whites. Conclusion: Our study highlights the importance of research methodology designed to improve non-response or response incompleteness, particularly in non-Hispanic blacks, as we move to reduce racial/ethnic disparities and strive to explain how and why disparities occur in the SCI population.