Background. Patients with neck pain, headache, torticollis, or neurological signs should be screened carefully for upper cervical spine instability, as these conditions are "red flags" for applying physical therapy interventions. However, little is known about the diagnostic accuracy of upper cervical spine instability tests. Purpose. The purpose of this study Was to evaluate the diagnostic accuracy of upper cervical spine instability screening tests in patients or people who are healthy. Data Sources. PubMed, CINAHL, EMBASE, and RECAL Legacy databases were searched from their inception through October 2012. Study Selection. Studies were included that assessed the diagnostic accuracy of upper cervical instability screening tests in patients or people who are healthy and in which sensitivity and specificity were reported or could be calculated using a 2 X 2 table. Data Extraction and Quality Assessment. Two reviewers independently performed data extraction and the methodological quality assessment using the QUADAS-2. Data Synthesis. Depending on heterogeneity, statistical pooling was performed. All diagnostic parameters (sensitivity, specificity, predictive values, and likelihood ratios) were recalculated, if possible. Results. Five studies were included in this systematic review. Statistical pooling was not possible due to clinical and statistical heterogeneity. Specificity of 7 tests was sufficient, but sensitivity varied. Predictive values were variable. Likelihood ratios also were variable, and, in most cases, the confidence intervals were large. Limitations. The included studies suffered from several biases. None of the studies evaluated upper cervical spine instability tests in patients receiving primary care. Conclusions. The membranes tests had the best diagnostic accuracy, but their applicability as a test for diagnosing upper cervical spine instability in primary care has yet to be confirmed.