We introduce a technique for patient mix‐adjusting $$\bar x$$ charts and compared differences between unadjusted and patient mix‐adjusted results. Our data came from coronary artery bypass graft (CABG) surgery patients at Baptist Medical Center, Oklahoma City, Oklahoma. We first developed an unadjusted $$\bar x$$ control chart to compare monthly changes in CABG surgery costs and then used a published model to patient mix‐adjust our $$\bar x$$ control chart information. Before adjustment, the average log costs for three of ten months were outside the 90% control limit lines, and there was a trend toward increasing costs. After adjustment, two months had average costs outside the 90% lower control limit lines, and the trend toward increasing costs had been explained by differences in patient acuity.