Background: Bioactive coating of uncemented total knee arthroplasty (TKA) is believed to increase bone ingrowth and enhance early fixation of the TKA. In a prospective randomized study using radiostereometric analysis (RSA) we examined migrations of the tibial implant, in an uncemented TKA with and without bioactive coating. The study was performed according to new RSA guidelines, and focus was put on some important methodological issues. Materials and methods: Twenty-three patients with osteoarthrosis of the knee received an uncemented Duracon TKA either with bioactive (hydroxyapatite or periapatite) coating (+HA) or without bioactive coating (-HA). Patients had RSA examinations postoperatively and at 3, 6 and 12 months. Nine patients were excluded during the study resulting in 14 knees for final analysis. Results: At 12 months follow-up we found no significant differences in migrations between the two groups. However, in general the -HA group migrated more than the +HA group, and we found a significant larger variation in migration pattern in the -HA group. In the +HA group the tibia component stabilized after 6 months, whereas the -HA group showed continuous migration. Subsidence and posterior tilt were the main migration patterns in both groups. Conclusions: Bioactive coating of TKA seems to enhance early stabilization of the tibia component. Similar results are found in previous studies.