Evaluation of patient-relevant treatment benefit gains importance for approval and reimbursement of therapeutic strategies. The 'Patient Benefit Index' (PBI) is the first questionnaire to measure patient-relevant treatment benefit in dermatology. Its global score is the average of benefits achieved after treatment, weighted by the individual importance of treatment needs. This study aimed to establish subscales of the PBI on the basis of independent and consistent treatment need dimensions. The PBI was used in a cross-sectional study involving n = 500 patients with ten distinct skin diseases, and in a longitudinal acne therapy study (n = 925). PBI dimensions were extracted by factor analysis and varimax rotation in both studies independently, using the longitudinal study data for replication. Factor analysis revealed largely similar need dimensions in both studies. The five-dimensional solution found in the cross-sectional study explained 63.0% of the variance. The need dimensions were named as reducing psychological impairments, reducing social impairments, reducing impairments due to therapy, reducing physical impairments, and building confidence into therapy. Using this factor solution, different patterns of need were found amongst the ten dermatological diseases. The PBI allows for a differential benefit assessment on five well distinguishable and interpretable subscales. The use of subscales as shown refines the interpretation of needs and benefits in dermatologic treatment.