OBJECTIVES: The utilization of health-related quality of life (HRQoL) questionnaires in the routine clinical practice is hampered by several factors, including their length and thus the time needed to complete and score them. For this reason, growing efforts are devoted both to create short questionnaires and to shorten existing ones. The Skindex-17 is a dermatological HRQoL instrument that was derived from the Skindex-29 using Rasch analysis. It is constituted by 17 items instead of 29 and answers are given on a three-point scale instead of five. The aim of this study was to compare information obtained by the Skindex-29 and the Skindex-17 in a large sample of dermatological outpatients. METHODS: We compared the Skindex-29 with the Skindex-17 scores in 2487 patients with several dermatological conditions, using the intraclass correlation coefficients.To verify that responses to individual items were affected by diagnosis in a comparable way in the two instruments we performed a Differential Item Functioning (DIF) analysis on random subsamples (n=230) of our study population RESULTS: The overall correlation was 0.957 for the symptoms scale and 0.940 for the psychosocial scale. The values were very similar for all the diseases. The concordance between the levels of severity of the Skindex subscales in the two instruments was also very high. Although several items of the Skindex-17 showed a significant DIF, it is to note that in all cases the corresponding Skindex-29 items also had a significant DIF. CONCLUSIONS: In conclusion, the Skindex-17 provided very similar information compared to the Skindex-29, with the advantage of being shorter and to fit some important psychometric properties.