Early results with the Mecron prosthesis have been variable. We report our experience with this prosthesis at medium- to long-term follow-up. At 5 to 9 years after surgery, 43 patients (49 implants) were reviewed. Radiographic measurements of superior migration, alteration in the opening angle, and thread engagement were made. The failure rate was very high, 33% having been revised or awaiting revision. Of the remainder, 80% had migrated, 86% had changes in the opening angle, and 65% had fewer threads engaged. Many have low-grade symptoms insufficient to merit revision, but the extent of loosening makes eventual revision likely. We feel this represents an example of a new design gaining widespread usage before adequate follow-up studies.