The Davidson Trauma Scale (DTS) is a validated 17-item self-rating scale used in the diagnosis of post-traumatic stress disorder (PTSD), which is sensitive to the effects of treatment. It was felt that a shorter version of the scale might provide a better diagnostic screening tool. Subjects were drawn from a sample of 243 patients obtained from multiple cohorts that included a group of survivors of various forms of trauma, including natural disaster, rape and combat. All subjects had diagnostic assessments for PTSD with a clinical interview and completed the DTS. The data were randomly divided between two subsamples, and frequency and severity scores were calculated for the DTS. A four-item scale, the SPAN (named for its top four items: Startle, Physiological arousal, Anger, and Numbness), was developed. It demonstrated an efficiency of 0.88, sensitivity of 0.84, specificity of 0.91 and positive likelihood ratio of 9.1. In a replication sample, values were slightly lower but still acceptable (efficiency = 0.80). A subgroup of PTSD patients received either fluoxetine or placebo in a clinical trial, and a significant SPAN score improvement was observed on fluoxetine. The SPAN, which correlated significantly with the Impact of Events Scale, the Sheehan Disability Scale, and the Structured Interview of PTSD, was found to have a diagnostic accuracy of 88%.