Drainage is a common procedure in unicompartmental knee arthroplasty (UKA), but evidence regarding its effectiveness is lacking. The aim of this study was to investigate the benefits of drainage after minimally invasive UKA with effective blood loss management. This was a prospective, randomized, controlled trial to determine whether drainage after UKA provides benefits with respect to blood loss, drainage volume, complications, pain score, knee score, range of motion and cost. The 96 patients who underwent surgery between January 2012 and March 2013 were randomly divided into two groups: group A (n = 48) was treated without drainage, and group B (n = 48) with drainage. All UKA procedures were performed with the same minimally invasive surgical technique. Tranexamic acid and bone wax were used for the management of blood loss in all patients. The preoperative baseline parameters of the two groups did not differ significantly. The mean drainage volume in group B was 75.7 +/- A 51.2 mL when the drainage was present. Total blood loss in group A and group B was 240.3 +/- A 73.3 mL and 274.1 +/- A 99.5 mL, respectively. These amounts did not differ significantly but both were significantly lower than the data reported for total knee arthroplasty. There was no difference in mean postoperative hemoglobin and hematocrit between groups. Differences in wound infection, incidence of deep vein thrombosis, postoperative Hospital for Special Surgery knee score, visual analog score, and range of motion were not statistically significant between groups. Hospitalization costs for UKA were lower in the absence of drainage. The use of drainage in unilateral UKA provides no apparent advantage. With effective blood loss management and a minimally invasive procedure, blood loss and drainage volume in UKA are very low. Drainage does not improve the results. Foregoing non-drainage after UKA reduces both hospital costs and visible blood loss. Therefore, drainage is unnecessary in routine UKA.