To evaluate the extent and severity of skin lesions in clinical trials enrolling dogs with atopic dermatitis (AD), the International Task Force on Canine Atopic Dermatitis recently recommended the use of the third version of the CADESI. This version of the CADESI was found to exhibit acceptable content, construct, criterion, inter- and intraobserver reliability and sensitivity to change. The current study was aimed at determining optimal CADESI-03 cut-off points to separate AD severity categories for future clinical trials. One hundred and eight dogs with AD were selected based on current diagnosis standards. At one or more visits, clinicians subjectively rated the severity of AD as ‘in remission’, ‘mild’, ‘moderate’ or ‘severe’, and a CADESI-03 score was then determined. In all, 158 CADESI-03 values were recorded and divided among the four disease severity categories. Receiver-operating characteristics (ROC) curves were generated at increasing cut-off values to determine the benchmark that would offer optimal sensitivity and specificity between adjacent categories. Cut-offs of 16, 60 and 120 are proposed at the interface of remission, mild, moderate and severe categories, respectively. Proposed intervals therefore are: remission: 0–15; mild AD: 16–59; moderate AD: 60–119; and severe AD: ≥ 120. This Task Force recommends that, whenever applicable and relevant, subgroup analyses of outcome measures, based on disease severity as determined with these cut-off CADESI-03 values, be preplanned for clinical trials enrolling dogs with AD. Such subgroup analyses could help determine whether specific interventions might be more effective in a particular subset of atopic dogs.