Abstract This study describes and compares the perceived sickness-related behavioral dysfunction of 859 end-stage renal disease (ESRD) patients from 11 centers according to treatment modality via the Sickness Impact Profile (SIP). The unadjusted functional status of ESRD patients differed significantly by treatment modality. Transplantation patients were least functionally limited followed in order by home dialysis, continuous peritoneal dialysis, and in-center dialysis patients. The largest overall differences were for the sleep and rest, work, recreation and pastimes, and home management SIP categories. Regression analysis revealed that many of the large observed intermodality differences in functional status may have resulted from casemix variations (e.g. age and comorbidity differences). Only SIP score differences between transplantation and other treatment modality patients remained significant following the introduction of casemix controls. Results do not justify choosing one dialysis modality over another because of differences in perceived dysfunction.