The aim of this prospective long-term clinical trial was to verify the clinical success of prefabricated precision attachments with regard to periodontal condition, wearing comfort, and stability of attachment friction. Twenty-eight patients were fitted with 35 prostheses with Swiss Mini-SG precision attachments. Following clinical investigation and monitoring over a 3-year period, 80% of the prostheses were functioning well. The average pocket depth of the abutment teeth at the buccal sites and the periodontal parameters Approximal Plaque Index and Sulcus Bleeding Index showed statistically significant improvements. The abutment tooth mobility (Periotest measurements) decreased. It is not advisable to support the attachments on single abutment teeth.