Background/aims: The International Contact Dermatitis Research Group (ICDRG) system for clinical scoring of allergic patch test reactions is well established in clinical dermatology for detailed scoring of allergic reactions. The degree of redness and the presence of swelling, papules, vesicles and bullae are assessed based on visual examination and palpation of reactions. In photographic assessment used in research and tele-dermatology, the scoring is solely based on visual examination of photos. The aim of the study was to evaluate inter-expert variation in patch test reading using photographic images, with ICDRG reading as a reference. Material and methods: Five experienced senior dermatologists each scored 55 positive patch test reactions from 16 slides in an office environment. The slides showed pictures of patch tests with different allergens. The scoring system by ICDRG with six categories for scoring was used. Results: The five dermatologists performed the scoring very differently. When the scoring system was simplified to a tripartite scoring system, the scoring was performed almost similarly by the five clinicians. Conclusion: Based on the present results, it is proposed that the number of scoring categories should be minimized and simplified into negative (including doubtful) reactions, positive reactions and irritant reactions. Such simplified tripartite reading is proposed for research purposes and for tele-dermatology, when scoring is based on photographic images. © Blackwell Munksgaard 2007.