With the publication of the Diagnostic and Statistical Manual of Mental Disorders, fifth edition, the American Psychiatric Association published several disorder-specific severity measures to support a dimensional approach to disorder classification. The Severity Measure for Specific Phobia – Adult (SMSP; Craske et al., 2013) was designed to provide a dimensional assessment of specific phobia symptoms, but limited psychometric data is currently available for this tool. This study assessed the construct and criterion validity of the SMSP in a sample of adults (n = 67) who self-reported specific phobia symptoms. The SMSP demonstrated excellent internal consistency (Cronbach’s α = 0.93) and statistically significant positive correlations were observed between the SMSP and an associated measure of specific phobia and distress. Statistically significant group differences were observed based on the outcome of a telephone-administered psychodiagnostic interview, such that SMSP scores were higher for participants who met diagnostic criteria for specific phobia than participants who did not (p < .001, d = 1.30). Regression models based on the outcome of the telephone interview indicated that scores on the SMSP uniquely predicted the presence or absence of specific phobia (p < .001) compared to scores from a hypothesized discriminant measure of depression (p = .67). Results provide support for the psychometric utility of the SMSP, though further evaluation of the construct validity of this measure in larger and more diverse samples is warranted.