96 patients scheduled for unicompartmental knee arthroplasty (UKA) were randomized to receive drainage or no drainage after surgery. The purpose of this study was to determine if there are any significant differences between drainage and no drainage after UKA for perioperative haematological outcomes or 1-year clinical outcomes. Significant differences were observed for visible blood loss, which was significantly lower in the no drainage group compared to the drainage group. There were no significant differences between groups for total blood loss, hemoglobin and hematocrit levels, knee swelling over the first 5 postoperative days, complications, or clinical outcomes at 1 year. The use of drainage significantly increased the cost of the operative compared to no drainage.