Casemix is a tool that classifies patients according to their clinical similarity and the homogeneity of resources required. A descriptive study was conducted to assess the level of knowledge and attitude toward the casemix-based funding system among staff working in the Iranian Social Security Organization in Tehran. The survey showed that knowledge of casemix and diagnosis-related groups (DRG) was poor among the study group and any attempt to implement the casemix system--which about three-quarters of high-level staff had never heard of--would be likely to fail. This highlights the necessity for creating awareness of the casemix and DRG systems among the hospital staff before any action takes place.