We developed a new version of the Social Phobia and Anxiety Inventory (SPAI) in order to have a brief instrument for measuring social anxiety and social anxiety disorder (SAD) with a strong conceptual foundation. In the construction phase, a set of items representing 5 core aspects of social anxiety was selected by a panel of social anxiety experts. The selected item pool was validated using factor analysis, reliability analysis, and diagnostic analysis in a sample of healthy participants (N=188) and a sample of clinically referred participants diagnosed with SAD (N=98). This procedure resulted in an abbreviated version of the Social Phobia Subscale of the SPAI consisting of 18 items (i.e. the SPAI-18), which correlated strongly with the Social Phobia Subscale of the original SPAI (both groups r=.98). Internal consistency and diagnostic characteristics using a clinical cut-off score>48 were good to excellent (Cronbach's alpha healthy group=.93; patient group=.91; sensitivity: .94; specificity: .88). The SPAI-18 was further validated in a community sample of parents-to-be without SAD (N=237) and with SAD (N=65). Internal consistency was again excellent (both groups Cronbach's alpha=.93) and a screening cut-off of >36 proved to result in good sensitivity and specificity. The SPAI-18 also correlated strongly with other social anxiety instruments, supporting convergent validity. In sum, the SPAI-18 is a psychometrically sound instrument with good screening capacity for social anxiety disorder in clinical as well as community samples.