Purpose: To compare immediate and conventional loading protocols for fixed full-arch mandibular prostheses supported by immediate and nonimmediate implants. Materials and Methods: A prospective controlled nonrandomized study with 12 months of follow-up included patients requiring fixed full-arch rehabilitations supported by immediate and nonimmediate implants. Eighteen patients were treated with conventional loading (control group), and 18 were treated with immediate loading (test group). Each patient received four to six implants; implants with insertion torque 35 Ncm were excluded from the study and loaded conventionally. The following variables were assessed: implant success, biologic and prosthetic complications, success of the immediately loaded provisional prostheses, and marginal bone loss. Statistical analysis was performed with nonparametric tests (chi-square, Mann-Whitney, Kruskal-Wallis) with an alpha value of .05. Results: Thirtysix patients consecutively enrolled in the study. Two control group patients failing to attend control visits and 12 implants that did not achieve an insertion torque of 35 Ncm were excluded. The final sample consisted of 34 patients and 183 implants (98 test and 85 control implants). Implant success rates were 99.0% (test) and 97.6% (control). Within the test group, success rates for immediate and nonimmediate implants were 100% and 97.6%, respectively. Differences were not statistically significant. All immediately loaded prostheses were successful. Five provisional fixed prostheses presented with loosened screws; all control group patients reported discomfort with the provisional denture. Average bone loss was 0.71 mm (standard deviation 0.25 mm) in the test group and 0.60 mm (standard deviation 0.28 mm) in the control group. Conclusion: No significant differences were seen in implant success and peri-implant marginal bone loss between immediate and conventional loading of mandibular fixed full-arch prostheses supported by immediate and nonimmediate implants. Biologic and prosthetic complications were rare, and all immediately loaded provisional fixed prostheses performed successfully. Keywords: controlled clinical trial, full-arch prosthesis, immediate loading, immediate implants, loading protocols