The mobility of 50 osseointegrated implants, inserted for improvement of the support of dentures in edentulous lower jaws, was studied during a period of up to 3 years by means of mechano-electronic measurements. The results showed that 3 months after implantation osseointegrated implants have less quasi-static mobility than natural teeth without periodontal lesions. Under the stresses of mastication the mobility of osseointegrated implants continuously increases. After 2-3 years, implants show a similar mobility as natural teeth supporting comparable denture constructions. The Periotest readings of implants were significantly lower than those of natural teeth, largely independent of the date of mobility measurement. A prognosis of functional properties as well as predicting the impending loss of osseointegrated implants is possible with the aid of long-term mobility measurements.