Purpose: To compare the outcome of immediate non-occlusal loading and that of delayed implant loading in the bilateral replacement of single mandibular molars. Materials and methods: This study was designed as a randomised, controlled, split-mouth trial. Twenty patients with bilaterally missing first mandibular molars had one of the sites to be restored randomly assigned to be treated with immediately or conventionally loaded single implants. A total of 40 implants were bilaterally installed. All the implants were inserted in healed healthy bone with an insertion torque between 35 and 45 Ncm. One molar was restored with a non-occluding temporary crown within 24 h after implant placement, while the contralateral molar was restored with a definitive crown 4 to 5 months later, according to a two-stage procedure. Final restorations were provided 4 to 5 months after implant placement for all implants. Outcome measures were implant survival, complications, radiographic marginal bone-level changes, PPD and BOP. Results: No patients dropped out and no implant failed. Only minor prosthetic complications were observed (2 provisional acrylic crown fractures in the immediate loading group and 2 ceramic chipping in the delayed loading group). Mean marginal bone loss was 0.83 ± 0.16 mm (95% CI 0.75 to 0.91) in the immediate loading group and 0.86 ± 0.16 mm (95% CI 0.78 to 0.94) in the conventional loading group and no statistically significant differences between the two groups were observed (P = 0.530). Mean PPD and BOP values were, respectively, 2.76 ± 0.48 (95% CI 2.55 to 2.97) and 1.30 ± 0.73 (95% CI 0.98 to 1.62) in the immediate loading group, and 2.70 ± 0.37 (95% CI 2.54 to 2.86) and 1.40 ± 0.75 (95% CI 1.07 to 1.73) in the conventional loading group. Also, a statistical comparison of BOP and PPD did not show any significant difference (P = 0.163 and P = 0.652, respectively). Conclusions: Within the limitations of this study, the present data seem to confirm the hypothesis that the clinical outcome of immediate versus delayed loading of implants in single mandibular molar sites is comparable. Schlagwörter: delayed loading, immediate loading, single lower tooth