Length of stay (LOS) benchmarking is a means of comparing hospital efficiency. Analysis of private cases in private facilities using Australian Institute of Health and Welfare (AIHW) data shows interstate variation in same-day (SD) cases and overnight average LOS (ONALOS) on an Australian Refined Diagnosis Related Groups version 4 (ARDRGv4) standardised basis. ARDRGv4 standardised analysis from 1998-99 to 2003-04 shows a steady increase in private sector SD cases (approximately 1.4% per annum) and a decrease in ONALOS (approximately 4.3% per annum). Overall, the data show significant variation in LOS parameters between private hospitals.