Purpose: The aim of this study was to develop and test the validity and inter-rater reliability of an instrument for describing IAD and its severity. Method: Investigators consulted two certified wound ostomy continence nurses (CWOCNs) expert in assessing perineal skin to determine face validity of the initial IAD instrument. Seven additional CWOCNs rated the degree of severity of the IAD descriptors to develop a scoring mechanism. Four case scenarios were developed to test the tool. The tool was tested, using the case scenarios, by 247 attendees at the 2007 National WOCN Society Conference (mean(sd) age=51(8) years, WOC experience= 25(9) years), and 100 staff at a care system in MN: 84 staff nurses (age=43(12) years, experience = 17(12) years), and 16 nursing assistants (age= 32(11), experience = 7(7) years). Inter-rater reliability was determined by comparing rater scores using a Kruskal-Wallis ANOVA and an intraclass correlation. Criterion validity was determined by comparing IAD severity scores of raters with those of the experts. Results: IAD scores for the four cases ranged from 3 to 27 and differentiated degrees of IAD severity. There were no significant differences in scores of IAD severity for the four cases among the three types of raters (p>.05). Overall agreement among the 347 raters using intraclass correlation was .87, p<.001. Intraclass correlation coefficient between the mode score of the raters and experts was .98, p<.001. Conclusion: The tool for describing IAD severity had very good criterion validity and inter-rater reliability among different levels of nursing staff.