Purpose: The goal of this study was to evaluate the cumulative survival rate and marginal bone loss (MBL) of extra-short (5- and 6-mm-long) and short (6.5-mm-long) implants inserted into severely atrophic, partially edentulous posterior maxillae and mandibles that were immediately restored with provisional fixed dental prostheses. Materials and Methods: Between October 2013 and December 2017, partially edentulous patients with severe vertical bone atrophy in the posterior area in need of replacement of premolars and/or molars with fixed prostheses were enrolled in the study. Analysis of cumulative survival rate and MBL was determined with respect to implant length at the longest, biannual follow-up period (38 ± 10 months; range: 25 to 48 months). Results: Fifty-five patients were included in the study. A total of 62 extra-short (5 and 6 mm), 15 short (6.5 mm), and 69 standard-length (≥ 10 mm) implants were immediately placed and loaded. Cumulative survival rates were similar for all implants (99.3%). One mandibular extra-short implant failed and was removed but was replaced 2 months later with another implant of the same length and diameter and successfully reloaded. Implant length did not impart any significant differences in MBL, though the presence or absence of platform switching was influential. Conclusion: The cumulative survival rate and MBL reported in this study encourage the use of short and extra-short implants to immediately restore with fixed prostheses partially edentulous patients with severe vertical bone atrophy in posterior areas. Thus, it could be an alternative treatment to vertical bone augmentation. Keywords: immediate restoration, implant-supported prosthesis, occlusal loading, posterior edentulism, short implants