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.