Purpose: To assess the clinical performance of single crowns in the posterior maxilla supported by either 11-mm-long implants combined with maxillary sinus floor elevation surgery or 6-mm-long implants during a 5-year follow-up period. Materials and methods: A total of 38 consecutive patients, missing a premolar or a molar in the posterior maxilla and residual bone height underneath the maxillary sinus between 6 to 8 mm, were included. Subjects were randomly allocated to receive one 11-mm-long implant in combination with maxillary sinus floor augmentation or to receive one 6-mm-long implant without any grafting. A total of 41 implants (21 implants in 20 patients in the 6-mm group, and 20 implants in 18 patients in the 11-mm group) were placed and subsequently restored after 3 months with custom-made titanium abutments and cemented zirconia-based porcelain crowns. Both groups were followed by clinical (implant survival, restoration survival, complications, pocket probing depth and presence of plaque, calculus, bleeding and peri-implant inflammation) and radiographic examinations up to 5 years. The patient satisfaction was scored before treatment, and 12 and 60 months after functional implant restoration. Results: One patient (11-mm group) died before the 12-month evaluation and one patient (6-mm group) moved away. In addition, one patient in the 6-mm group lost one implant and no implants were lost in the 11-mm group. Two patients lost three restorations in the 6-mm group and no restorations were lost in the 11-mm group. From loading until the 60-month assessment, the mean marginal bone loss in the 6-mm group and the 11-mm group was 0.12 ± 0.36 mm and 0.14 ± 0.63 mm, respectively, without a significant difference (mean difference 0.02 mm; 95% CI -0.32 to 0.37; P = 0.884). Implant loss, restoration loss, screw loosening and porcelain chipping were defined as complications. Four patients in the 6-mm group and one patient in the 11-mm group had one or more complications, without a significant difference between the groups (95% CI 0.019 to 0.244; P = 0.198). The patient satisfaction was high in both groups (mean overall satisfaction in the 6-mm and the 11-mm groups was 9.4 ± 0.8 and 9.2 ± 0.8, respectively; mean difference 0.2; 95% CI -0.33 to 0.76; P = 0.434). Conclusions: Reconstructions performed using an 11-mm implant combined with maxillary sinus floor augmentation or a 6-mm implant in the resorbed posterior maxilla are equally successful in supporting a single restoration over 5 years.