Introduction: The aim of this study was to evaluate and compare the clinical success of 2 lingual retainer wires. Methods: The 120 patients included in the study were divided into 2 groups randomly. In group 1, 0.0175-in 6-strand stainless steel wire (Ortho Technology, Lutz, Fla) was used, the lingual retainers were fabricated on plaster models, and a silicon transfer key was used. In group 2, 0.0195-in dead-soft coaxial wire (Respond; Ormco, Orange, Calif) was used, and the lingual retainers were fabricated directly in the patient's mandibular arch without a study model. Pretreatment, posttreatment, and posttreatment 3-month, 6-month, 9-month, and 12-month 3-dimensional orthodontic models were evaluated. Failure rates, mandibular arch irregularity values, intercanine distances, and arch lengths were compared. Results: The clinical bond failure rates were 13.2% for the 0.0175-in 6-strand stainless steel wire and 18.9% for the 0.0195-in dead-soft wire. The difference in bond failures between the 2 groups was not statistically significant. There was a statistically significant increase in mandibular arch irregularity in both groups during the 12-month follow-up. However, the increase was significantly higher in the second group than in the first one. Furthermore, the intercanine distance decreased over time in the second group. Conclusions: Our findings regarding mandibular arch measurements indicate that fabrication of lingual retainers can be more safely accomplished with 0.0175-in 6-strand stainless steel wire than with 0.0195-in dead-soft coaxial wire.