Purpose: The aim of this randomised controlled trial was to assess the clinical performance of single crowns in the posterior maxilla supported by either 6-mm or 11-mm implants combined with maxillary sinus floor elevation. Materials and methods: 41 consecutive patients with one missing premolar or molar in the posterior maxilla and with an estimated bone height of 6 to 8 mm in that area were included. Each patient was randomly allocated to one of the two treatment groups, namely to receive an 11-mm implant (OsseoSpeed 4.0S, Dentsply Implants, Mölndal, Sweden) in combination with maxillary sinus floor elevation surgery or to receive a 6-mm implant (OsseoSpeed 4.0S) without any grafting. After a 3-month osseointegration period, all implants were restored with custom-made titanium abutments and cemented zirconia-based porcelain crowns. Outcome measures were: implant survival; radiographic bone changes; plaque accumulation; bleeding tendency; peri-implant inflammation; presence of dental calculus; biological and technical complications; and patients' satisfaction. Clinical and radiographic examinations were performed at placement of the crown and 12 months thereafter. Patients' satisfaction was scored before treatment and after 12 months of functioning of the crown. Results: One patient of the 11 mm implant group died during the follow-up. No implant failed and no biological or technical complications occurred. From loading to the 12 months follow-up, no difference was found in mean marginal bone changes between the groups (bone resorption in both groups 0.1 ± 0.3 mm). Clinical items revealed very healthy peri-implant soft tissues in both groups. Patients' satisfaction scores were high in both groups. Conclusions: 6-mm implants and 11-mm implants combined with sinus floor elevation surgery are equally successful to support a single crown in the resorbed posterior maxilla after 1-year follow-up.