This prospective study assessed 54 consecutive arthroscopically assisted ACL reconstructions for the amount of postoperative pain relief provided by cold therapy, using the Hot/Ice Thermal Blanket. Twenty-six randomly selected patients undergoing this procedure were compared to a control group consisting of 28 patients having the identical procedure in which the Hot/Ice unit was not used postoperatively. The initial ACL injury in both groups was sports related with the exception of three patients whose injury occurred while on the job. The Hot/Ice Thermal Blanket consists of two rubber pads (blankets) connected by a hose to the main cooling unit. The pads were applied to either side of the operated knee in the operative suite. The pads received fluid which was circulated from the main unit. The temperature of the fluid was set at 50 degrees in the recovery room and the unit was run continuously until the time of discharge, which was approximately 4 days. Hot/Ice patients required 53% less injectable Demerol and 67% less oral Vistaril than patients in the control group. Hot/Ice patients had made the conversion from injectable to oral pain medication an average of 1.2 days sooner than did their non-Hot/Ice counterparts. There was no appreciable difference in length of hospital stay. Physical therapy and nursing records documented a greater percentage of compliant patients in the Hot/Ice group. According to these records the Hot/Ice patients were more helpful in self-assistance, were out of bed and ambulating in the halls more quickly, and did their range of motion exercises with greater ease.(ABSTRACT TRUNCATED AT 250 WORDS)