Twenty-one ankle replacements in nineteen patients after an average follow-up of 14.7 months were analyzed with respect to their history, physical and roentgenographic findings, and gait analysis. The relief of pain and functional improvement after operation were disappointing compared with the results of prosthetic replacement in other joints and were not related to early complications, age, diagnosis, or the prosthesis used. Muscle weakness about the ankle, especially of the plantar flexors, was a prominent finding and appeared to cause abnormal patterns of gait and of ankle motion. The frequency of progressively increasing radiolucent lines was 88 per cent and of late loosening, 10 per cent. These results suggest a need for more emphasis on postoperative rehabilitation and on the uncertainty of this procedure at its present stage of development.