We describe the development of a new self-report instrument, the Social Anxiety and Depression Life Interference-24 (SADLI-24) inventory. We initially retained 30 content specific items for the instrument (Study 1). In Study 2 (N = 438), we established a 2-factor solution, Social Anxiety Life Interference-12 (SALI-12) and Depression Life Interference-12 (DLI-12). We also examined estimates of known-groups and concurrent validity. Confirmatory factor analysis in Study 3 (N = 430) provided support for the oblique two-factor structure. In Study 4 (N = 179), we provided additional support for estimates of known-groups validity. In Study 5 (N = 63), we evaluated estimates of test-retest reliability. Both SADLI-24 scale scores showed good estimates of internal consistency. © 2010 Wiley Periodicals, Inc. J Clin Psychol 67:1–17, 2010.